Patent Publication Number: US-10775906-B2

Title: Power source for biometric enrollment with status indicators

Description:
CROSS REFERENCE OF RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. § 119(e) of the filing dates of U.S. provisional patent application Ser. No. 62/597,674 filed Dec. 12, 2017, U.S. provisional patent application Ser. No. 62/627,398 filed Feb. 7, 2018, and U.S. provisional patent application Ser. No. 62/767,338 filed Nov. 14, 2018 the respective disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates to a fingerprint sensor installed on a device that has limited ability to provide feedback to a user or obtain instructions from the user, such as, for example, smart cards, fitness monitors, wearables, domestic and industrial appliances, automotive components, and “internet of things” (IOT) devices. 
     BACKGROUND 
     In the electronic sensing market, there are a wide variety of sensors for sensing objects at a given location. Such sensors are configured to sense detectable and/or measurable characteristics of an object in order to sense the presence of an object near or about the sensor and other features and characteristics of the object being sensed. Such “sense characteristics” may include a variety of detectable characteristics, such as electronic, electromagnetic, ultrasonic, thermal, optical characteristics, among others. 
     It is now common to see fingerprint sensors installed on devices such as smartphones. A fingerprint sensor installed on a smart phone can be used to verify the identity of the user. The fingerprint sensor can also be used as a data entry or a control mechanism for the smart phone. For example, the fingerprint sensor can detect a position of the finger on its surface and translate the position of the finger as an instruction to select a function of the smart phone or to navigate within menus being displayed by the smart phone. 
     As fingerprint sensors are gaining in recognition and user acceptance, fingerprint sensors are finding use in numerous other devices such as a smart cards, fitness monitors, wearables, domestic and industrial appliances, automotive components, and internet of things (IOT) devices. Some devices, such as smart cards and IOT devices, have limited to no user interfaces or status indicators such as screens, speakers, LEDs, and audio signals. Such devices may also have limited to no user input mechanisms in order to receive user input due to an absence of a keyboard, switches, buttons, and levers. 
     Accordingly, there is a need for a fingerprint sensor installed on a device with limited ability to provide feedback to or obtain instructions from a user wherein the fingerprint sensor provides a data entry or a control mechanism for the device. The fingerprint sensor may have a prime purpose of verifying the user&#39;s identity, but can also function as convenient way to control or enter data into a device with limited ability to provide feedback to or obtain instructions. 
     U.S. Pat. No. 7,129,926 “Navigation Tool,” the respective disclosure of which is hereby incorporated by reference, describes a navigation tool for connecting to a display device, comprising at least two sensor elements having known positions relative to each other, each sensor element being coupled to detector means for recording a change in a predetermined parameter and timing means for determining the time of change at each sensor element and calculating means for calculating the direction and speed of the recorded changes based on the relative positions of the sensor elements and the duration between the recorded changes. 
     International Patent Application No. PCT/NO02/00468, “Navigation Concept,” the respective disclosure of which is hereby incorporated by reference, describes an electronic unit, and method for providing input to the electronic unit, the unit comprising a sensor being capable of sensing direction of a movement over the sensor, and the method comprising the steps of: sensing the direction of a movement, categorizing the sensed direction into a chosen number of categories, said categories each being related to one or more signs, e.g., characters, on the ending of said movement, providing the related sign or command to the electronic unit as input. 
     U.S. Patent Application Publication No. 2014-0300574 “Biometric Sensing” the respective disclosure of which is hereby incorporated by reference, describes a dual grid touchscreen with clusters of drive and pick up lines resulting in an impedance sensor that operate in dual resolution processing modes, i.e., in low or high resolution mode, in order to track motion of an object creating a touch input. 
     SUMMARY 
     The following presents a simplified summary in order to provide a basic understanding of some aspects described herein. This summary is not an extensive overview of the claimed subject matter. It is intended to neither identify key or critical elements of the claimed subject matter nor delineate the scope thereof. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later. 
     In one example, a fingerprint sensor and data input system comprises a two-dimensional array of sensor elements, each sensor element being configured to generate a signal in response to a finger surface placed in detectable proximity to the sensor elements, and a processor configured to process signals generated by the sensor elements and to be selectively placed in a fingerprint sensing mode and a data input mode. In the data input mode, the processor is configured to determine in which of two or more spatially distinct regions of the array each sensor element that generates a signal in response to a finger surface placed in detectable proximity to the sensor element is located to effect a data input based on which spatially distinct region is contacted by the finger surface. In the fingerprint sensing mode, the processor is configured to detect variations in signals generated by sensor elements in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface and to form an image of the fingerprint of the finger surface. 
     In another example, a fingerprint sensor and data input system comprises a two-dimensional array of sensor elements, each sensor element being configured to generate a signal in response to a finger surface placed in detectable proximity to the sensor element, a data input device operatively placed on the array and defining two or more spatially distinct regions of the array, and a processor. The processer is configured to detect and distinguish contact with each of the two or more spatially distinct regions of the array when the data input device is operatively placed on the array and to detect variations in signals generated by sensor elements in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface and to form an image of the fingerprint of the finger surface when the data input device is not operatively placed on the array. 
     In another example, a fingerprint sensor and data input system comprises a two-dimensional array of sensor elements, each sensor element being configured to generate a signal in response to a finger surface placed in detectable proximity to the sensor element, a data input device operatively placed on the array and defining two or more spatially distinct regions of the array, and a processor. The processor is configured to detect and distinguish contact with each of the two or more spatially distinct regions of the array and to detect an authentication code entered by a user contacting the two or more spatially distinct regions in a specified sequence when the data input device is operatively placed on the array and to detect variations in signals generated by sensor elements in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface and to form an image of the fingerprint of the finger surface after a correct authentication code has been detected. 
     In another example, a method for enrolling a fingerprint with a two-dimensional array of sensor elements—each sensor element being configured to generate a signal in response to a finger surface placed in detectable proximity to the sensor element—comprises detecting contact by a user&#39;s finger with different spatially distinct regions of the array of sensor elements, detecting a code entered by the user contacting different spatially distinct regions of the array in a sequence, and authenticating the detected code if it matches a predefined activation code, and, if the detected code matches the predefined activation code, storing one or more fingerprint images formed when the user places a finger on the array of sensor elements. 
     In another example, a device comprises a sensor with a removable data input device over the sensor. The removable data input device comprises a pattern of windows defining spatially distinct regions of the sensor. 
     In another example, a fingerprint sensor and data input system comprises a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element, a data input device operatively coupled to the array and including two or more data input keys, each key being associated with one or more spatially distinct data input regions of the array, and a processor. The processor is configured to detect and distinguish contact with each data input key via a signal produced by the one or more spatially distinct data input regions of the array associated with that data input key when the data input device is operatively coupled to the array and to detect variations in signals produced by sensor elements in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface and to form an image of the fingerprint of the finger surface when the data input device is not operatively coupled to the array. 
     In another example, a fingerprint sensor and data input system comprises a fingerprint sensor comprising an array of capacitive sensor elements, each sensor element being configured to produce a contact signal when contacted by a finger and a data input device configured to be removably attached to a host device incorporating the fingerprint sensor and including two or more data input keys. Each data input key is remotely coupled with one or more associated data input regions of the array so that the sensor elements encompassed by the associated data input region produce a contact signal when a user touches the data input key. 
     In another example, a data input system comprises a host device with a sensor and a data input device removably disposed over the sensor. The data input device comprises two or more data input keys, and each data input key is associated with one or more spatially distinct data input regions of a sensing area of the sensor. 
     In another example, a data input device that is removably attachable with respect to an array of contact sensor elements comprises two or more data input keys remotely disposed with respect to a portion of the data input device covering the array, each data input key comprising a conductive key trace disposed on the data input device, a conductive sensing area activation trace associated with each data input key and configured to be disposed over a spatially discrete portion of the array when the data input device is removably attached with respect to the array, and a conductive connecting trace electrically connecting each conductive key trace with the associated sensing area activation trace. 
     In another example, a method for enrolling a fingerprint on a smart card containing a fingerprint sensor comprises connecting the smart card to a power source, entering an activation code by using a finger to contact two or more data input keys of a data input device attached to the smart card in a sequence corresponding to the activation code, wherein a portion of the data input device is positioned over a sensing area of the fingerprint sensor and each data input key is associated with one or more spatially distinct data input regions of the sensing area, removing a portion of the data input device from the smart card to uncover the sensing area of the fingerprint sensor, contacting the sensing area of the fingerprint sensor one or more times with a finger to enroll a fingerprint template (i.e., a verification template of biometric data), and disconnecting the smart card from the power source. 
     In another example, a smart card comprises a card body capable of deflection along any axis lying in the plane of the card, a fingerprint sensor for authenticating a user of the smart card, a data storage element storing an activation code, a data input device coupled to the fingerprint sensor to associate distinct areas of the data input device with distinct areas of the fingerprint sensor, each distinct area of the sensor corresponding to a uniquely identifiable portion of an activation code, and a processor configured to translate a code input by a user interacting with the fingerprint sensor via the data input device and to compare the code input by the user with the stored activation code. 
     In another example, a method for enrolling a fingerprint sensor comprises defining an activation code to initiate an enrollment process for the fingerprint sensor and enabling a user to enter the activation code into the fingerprint sensor by interacting with each of two or more distinct portions of the fingerprint sensor. Each of the two or more distinct portions of the fingerprint sensor corresponds to a uniquely-identifiable portion of the activation code. 
     In another example a method for enrolling a fingerprint template (i.e., a verification template of biometric data) on a smart card having a fingerprint sensor comprises connecting one or more power transmission contacts of the smart card to a power source without connecting any data transmission contacts of the smart card to a device configured to transmit or receive data, automatically activating an enrollment mode in the fingerprint sensor upon a specific instance of connecting the one or more power transmission contacts of the smart card to the power source, enrolling a fingerprint by storing a fingerprint template derived from one or more fingerprint images generated by placing a finger on the fingerprint sensor, and upon completion of the enrolling step, automatically deactivating the enrollment mode in the fingerprint sensor. 
     In another example, a method for enrolling a fingerprint template on a smart card having a fingerprint sensor comprises connecting one or more power transmission contacts of the smart card to a power source without connecting any data transmission contacts of the smart card to a device configured to transmit data to or receive data from the smart card, determining if a fingerprint template has been enrolled for the fingerprint sensor of the smart card, if no fingerprint template has been enrolled for the fingerprint sensor of the smart card, automatically activating an enrollment mode in the fingerprint sensor upon connecting the one or more power transmission contacts of the smart card to the power source, enrolling a fingerprint by storing a fingerprint template derived from one or more fingerprint images generated by placing a finger on the fingerprint sensor, and upon completion of the enrolling step, automatically deactivating the enrollment mode in the fingerprint sensor. 
     In another example, a fingerprint sensor and data input system comprises a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element, a data input device, including a portion disposed over the array and including a pattern of piercings formed in the portion of the data input device disposed over the array, wherein the piercings are spatially associated with one or more spatially distinct data input regions of the array, and a processor. The processer is configured to detect a finger placed in contact with the associated spatially distinct data input regions of the array and to detect a pattern of signals produced by the spatially distinct data input regions contacted through the pattern of piercings. 
     In another example, a fingerprint sensor and data input system comprises a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element, a data input device, including a portion disposed over the array and including a pattern of conductive material applied to the portion of the data input device disposed over the array, wherein the pattern is spatially associated with one or more spatially distinct data input regions of the array, and a processor. The processor is configured to detect contact of the pattern of conductive material with the associated spatially distinct data input regions of the array and to detect a pattern of signals produced by the spatially distinct data input regions contacted by the pattern of conductive material. 
     In another example, a fingerprint sensor and data input system comprises a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element, a data input device partially disposed over the array and including two or more data input keys, each key being associated with one or more spatially distinct data input regions of a first portion of the array, and a cutout exposing a second portion of the array, and a processor configured to detect and distinguish contact with each data input key via a signal produced by the one or more spatially distinct data input regions of the array associated with that data input key and to detect variations in signals produced by sensor elements of the second portion of the array in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface. 
     In another example, a device including a fingerprint sensor and data input system and comprises a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element, two or more data input keys disposed on a portion of the device remote from the plurality of sensors, each data input key being coupled with one or more spatially distinct data input regions of a first portion of the array so that contact with the data input key results in a signal produced by sensor elements within each spatially distinct data input region coupled to the data input key, and a processor. The processor is configured to detect and distinguish contact with each data input key via a signal produced by the one or more spatially distinct data input regions of the array coupled with that data input key and to detect variations in signals produced by sensor elements of a second portion of the array in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface. 
     In another example, a method for enrolling a fingerprint on a smart card containing a fingerprint sensor comprises connecting the smart card to a power source, entering an activation code by using a finger to contact two or more data input keys of a data input device attached to the smart card in a sequence corresponding to the activation code, wherein a portion of the data input device is positioned over a portion of the sensing area of the fingerprint sensor, and each data input key is associated with one or more spatially distinct data input regions of a portion of the sensing area, contacting the portion of the sensing area of the fingerprint sensor that is not covered by a portion of the data input device one or more times with a finger to enroll a fingerprint template, and disconnecting the smart card from the power source. 
     In another example, a method for enrolling a fingerprint template on a smart card having a fingerprint sensor comprises connecting one or more power transmission contacts of the smart card to a power source without connecting any data transmission contacts of the smart card to a device configured to transmit or receive data, activating an enrollment mode in the fingerprint sensor upon detection of a trigger event, enrolling a fingerprint by storing a fingerprint template derived from one or more fingerprint images generated by placing a finger on the fingerprint sensor, and upon completion of the enrolling step, deactivating the enrollment mode in the fingerprint sensor. 
     In another example, the trigger event comprises one or more trigger events selected from the list consisting of a. user interactions with the biometric sensor assembly, b. placing a detectable object on the biometric sensor assembly, c. removing a detectable object from the biometric sensor assembly, d. detecting the absence of a stored verification template, e. detecting the presence of a stored verification template that is partially complete, f. detecting that power is being transmitted to the smart card for the first time, g. detecting a specified instance of power being transmitted to the smart card, h. detection that a maximum number of unsuccessful attempts to derive a verification template has not been reached, I. activating an input mechanism, j. expiration of a timer or counter, k. occurrence of an error state, l. detection of a flag set last time the smart card was inserted in a card reader that transmits data to or from the smart card, m. detection that the smart card has been connected to a power source that does not transmit data to or from the card, n. detection of a trigger event by a component of the smart card other than the biometric sensor assembly, and o detection that a particular smart card has been coupled to a particular non-data-transmitting power source. 
     In another example, a power source for a smart card comprises a power element, and a housing. The housing comprises a slot configured to receive an end of the smart card and contacts connected to the power element. The contacts contact power transmission contact pads of the smart card and do not contact data transmission contact pads of the smart card when the smart card is inserted into the slot to thereby connect the power transmission contact pads of the smart card to the power element. 
     In another example, an overlay is configured to provide power to an electronic device having terminals for connecting a source of electric power to the electronic device, and the overlay is configured to be removably secured to a surface of the electronic device. The overlay comprises a film configured to conform to the surface of the electronic device when secured thereto, a power element supported on the film, conductive material disposed on or embedded in a surface of the film, wherein the conductive material connects the power element to the terminals of the electronic device when the overlay is secured to the surface of the electronic device, and a circuit closure configured to enable a user to selectively close a power circuit between the power element and the terminals of the electronic device to enable power transmission between the power element and the electronic device. 
     In another example, a method for enrolling a biometric template on an electronic device having power terminals, data transmission terminals, and a biometric sensor comprises connecting an overlay to the electronic device, wherein the overlay is configured to provide power to the electronic device from a power element mounted on the overlay to the power terminals of the electronic device and to connect to the data transmission terminals of the electronic device, closing a power circuit between the power element and the power terminals of the electronic device to enable power transmission between the power element and the electronic device, triggering the biometric sensor to enter an enrollment mode, and generating the biometric template from biometric inputs from a user to the biometric sensor. 
     In another example, a finger guide is configured to be removably attached to a device having a fingerprint sensor and comprises two or more channels. Each channel is configured to position a finger placed thereon to contact the fingerprint sensor at a different orientation. 
     In another example, a power source and finger guide for a smart card including a fingerprint sensor comprise a power element, a card holder frame comprising one or more card guide rails into which the smart card is inserted to position the cardholder frame with respect to the smart card, and contacts connected to the power element, wherein the contacts contact power transmission contact pads of the smart card when the smart card is inserted into the card guide rail to thereby connect the power transmission contact pads of the smart card to the power element, and a finger guide attached to the card holder frame and comprising two or more channels, wherein each channel is configured to position a finger placed thereon to contact the fingerprint sensor at a different orientation. 
     In another example, a fingerprint sensor and data input system comprises a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element, a data input device partially disposed over the array and including two or more data input keys, each key being associated with one or more spatially distinct data input regions of a first portion of the array, and a cutout exposing a second portion of the array, a processor configured to detect and distinguish contact with each data input key via a signal produced by the one or more spatially distinct data input regions of the array associated with that data input key and to detect variations in signals produced by sensor elements of the second portion of the array in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface, and finger guide comprising two or more channels, wherein each channel is configured to position a finger placed thereon to contact the two-dimensional array at a different orientation. 
     In another example, a method for enrolling a fingerprint on a smart card containing a fingerprint sensor comprises connecting the smart card to a power source, entering into an enrollment mode upon determination of a trigger event, contacting the fingerprint sensor by placing the same finger on each of two or more finger guide channels configured to position the finger placed thereon in a unique orientation with respect to the fingerprint sensor to enroll a fingerprint template for that finger, and disconnecting the smart card from the power source after enrolling the fingerprint template. 
     In another example, a method for re-enrolling a fingerprint on a smart card containing a fingerprint sensor wherein at least one fingerprint template has been previously enrolled comprises A. connecting the smart card to a power source, B. entering into a re-enrollment mode upon determination of a trigger event, C. contacting the fingerprint sensor by sequentially placing the same finger on each of two or more finger guide channels configured to position the finger placed thereon in a unique orientation with respect to the fingerprint sensor to enroll a fingerprint template for that finger, D. replacing the previously enrolled fingerprint template with a new fingerprint template formed from fingerprint images generated during step C or updating the previously enrolled fingerprint template with fingerprint images generated during step C, and E. disconnecting the smart card from the power source. 
     In another example, a method for enrolling two or more fingerprints on a device containing a fingerprint sensor comprises A. connecting the device to a power source; B. entering into a first enrollment mode upon determination of a trigger event, C. enrolling a first fingerprint template for a first finger, D. entering a subsequent enrollment mode upon determination of a trigger event, E. enrolling a subsequent fingerprint template for a subsequent finger different from a previously enrolled finger; F. determining if a required number of fingers has been enrolled, G. if the required number of fingers has not been enrolled, return to step D, and H. if the required number of fingers has been enrolled, disconnecting the smart card from the power source. 
     In another example, a system for enrolling a verification template of biometric data in a biometric-enabled smart card comprises a non-data-transmitting power source configured to be coupled to the smart card to transmit power to the smart card without transmitting data to or from the smart card, wherein the non-data-transmitting power source comprises a power element and a receptacle configured to receive an end of the smart card, and a biometric sensor assembly comprising one or more sensor elements and associated circuitry for controlling operation of the one or more sensor elements and for processing signals from the one or more sensor elements. The biometric sensor assembly is configured to be installed in the smart card whereby power is transmitted to the biometric sensor assembly when the non-data-transmitting power source is coupled to the smart card. The biometric sensor assembly is configured to operate in an enrollment mode when power is transmitted to the biometric sensor assembly by the non-data-transmitting power source. When operating in enrollment mode, the biometric sensor assembly is configured to derive and store a verification template of biometric data from one or more biometric images generated by the one or more sensor elements. 
     In another example a method for enrolling a biometric template on a smart card having a biometric sensor comprises inserting an end of the smart card into a receptacle, transmitting power to the smart card from the receptacle without transmitting data to or from the smart card, causing the biometric sensor to operate in an enrollment mode, while the biometric sensor is operating in enrollment mode, generating one or more biometric images with the biometric sensor, deriving at least one verification template of biometric data from the one or more biometric images, storing the verification template, and after storing the verification template, terminating enrollment mode in the biometric sensor. 
     In another example, a device to facilitate the enrollment of a verification template of fingerprint data in a fingerprint sensor-enabled smart card, the device comprises a receptacle configured to be removably coupled to the smart card; a power element supported on the receptacle, wherein the receptacle is configured to transmit power from the power element to the fingerprint sensor of the smart card when the receptacle is coupled to the smart card; a finger guide attached to the receptacle and comprising two or more finger guide channels, wherein the finger guide is configured so that each finger guide channel is adjacent the fingerprint sensor of the smart card when the receptacle is coupled to the smart card, and wherein each finger guide channel is configured to position a finger placed thereon to contact the fingerprint sensor at a different orientation; and two or more status indicators, wherein each status indicator is associated with one finger guide channel and is configured to instruct the user with respect to the placement and removal of the user&#39;s finger with respect to the associated finger guide channel. 
     In another example, method for enrolling a fingerprint template on a smart card having a fingerprint sensor comprises: (A) transmitting power to the smart card from a power source removably coupled to the smart card, the power source including a power element that provides power to the fingerprint sensor and a finger guide comprising two or more finger guide channels positioned adjacent to the fingerprint sensor of the smart card when the power source is coupled to the smart card, and wherein each finger guide channel is configured to position a finger placed thereon to contact the fingerprint sensor at a different orientation; and (B) during step (A), instructing the user with respect to the placement and removal of the user&#39;s finger with respect to each finger guide channel with a status indicator associated with the finger guide channel. 
     Other features and characteristics of the subject matter of this disclosure, as well as the methods of operation, functions of related elements of structure and the combination of parts, and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments of the subject matter of this disclosure. In the drawings, like reference numbers indicate identical or functionally similar elements. 
         FIG. 1  illustrates a fingerprint sensor installed on a smart card according to some embodiments. 
         FIGS. 2A and 2B  are top views of a sensing area of the fingerprint sensor installed on a device according to some embodiments. 
         FIGS. 3A-3B  illustrate a data input device in the form of an overlay temporarily placed over the sensing area of the fingerprint sensor installed on a smart card according to some embodiments. 
         FIGS. 4A-4C  are top plan views of a data input device in the form of an overlay temporarily placed over the sensing area of the fingerprint sensor with different configurations of pierced holes according to some embodiments. 
         FIGS. 5A and 5B  illustrate a data input device in the form of a frame placed over the sensing area of the fingerprint sensor installed on a device according to some embodiments. 
         FIGS. 6A-6C  illustrate a data input device in the form of a double layered overlay which may be temporarily placed over the sensing area of the fingerprint sensor according to some embodiments. 
         FIG. 7A  illustrates a data input device in the form of an overlay with complex piercing patterns temporarily placed over the sensing area of the fingerprint sensor according to some embodiments. 
         FIG. 7B  illustrates a data input device in the form of an overlay with detectable printed patterns temporarily placed in contact with the sensing area of the fingerprint sensor according to some embodiments. 
         FIG. 8  illustrates a method of calibration for the fingerprint sensor according to some embodiments. 
         FIG. 9A  illustrates a power source used with the fingerprint sensor installed on the smart card according to some embodiments. 
         FIGS. 9B and 9C  show a bottom view and top view, respectively, of the power source according to some embodiments. 
         FIGS. 9D and 9E  show a perspective view and plan view, respectively, of an alternative card holder/power source according to some embodiments. 
         FIG. 9F  is a top perspective view of an alternative card holder/power source without a card disposed in the card holder according to some embodiments. 
         FIG. 9G  illustrates a transverse cross section of the card holder/power source along the line F-F in  FIG. 9F , with a card disposed in the card holder according to some embodiments. 
         FIG. 9H  illustrates a transverse cross section of a card holder/power source similar to  FIG. 9G  and showing an alternative card holder/power source according to some embodiments. 
         FIGS. 10A-10E  illustrate an embodiment of the power source in use with the fingerprint sensor installed on the smart card. 
         FIGS. 11A-11C  illustrate an embodiment of the power source in use with the fingerprint sensor installed on the smart card. 
         FIGS. 12A-12C  illustrate an embodiment of the power source in use with the fingerprint sensor installed on the smart card. 
         FIG. 13  illustrates a data input device in the form of an overlay which includes data input keys coupled to associated spatially distinct sensing areas on the sensing area of the fingerprint sensor according to some embodiments. 
         FIGS. 14A-14C  illustrate a data input device in the form of a multi-layer overlay including data input keys coupled to associated spatially distinct sensing areas on the sensing area of the fingerprint sensor according to some embodiments. 
         FIG. 15A  illustrates an embodiment of the data input device in the form of an overlay including data input keys coupled to associated spatially distinct sensing areas on the sensing area of the fingerprint sensor and including the use of spatially distinct reference areas of the sensing area that are not coupled to associated data input keys for noise cancellation. 
         FIG. 15B  illustrates an embodiment of the data input device in the form of an overlay including data input keys coupled to associated spatially discrete portions of the sensing area of the fingerprint sensor. 
         FIGS. 15C and 15D  illustrate magnified views of sensing activation traces placed over a sensing area according to some embodiments. 
         FIGS. 15E-15H  illustrate embodiments of conductive material arrangement on the data input device in the form of an overlay when temporarily placed over the sensing area of the fingerprint sensor. 
         FIGS. 16A-16B  illustrate embodiments of a data input device in which each key comprises two conductive elements, each coupled to an associated spatially distinct sensing areas on the sensing area of the fingerprint sensor, wherein contact with the key completes a circuit through the two conductive elements to ground. 
         FIG. 17  is a cross sectional view of an embodiment of a data input device in the form of a single layer overlay with data input keys coupled to associated spatially distinct sensing areas on the sensing area of the fingerprint sensor, wherein the key is located on a first side of the overlay and the overlay includes a conductive trace extending through the overlay to a conductive trace connected to an associated spatially distinct sensing area on an opposite side of the overlay. 
         FIG. 18  is a cross sectional view of an embodiment of a data input device in the form of an overlay secured to opposed sides of a host device and including data input keys on multiple surfaces of the host device that are coupled to associated spatially distinct sensing areas on the sensing area of the fingerprint sensor. 
         FIG. 19  illustrates an embodiment of a data input device including data input keys on a remote keypad device and a data transfer cable coupling the data input keys to associated spatially distinct sensing areas on the sensing area of the fingerprint sensor. 
         FIG. 20  illustrates an embodiment of a data input device including data input keys coupled to associated spatially distinct sensing areas on the sensing area of the fingerprint sensor, wherein the data input keys are remotely located from the sensing area and the data input device extends off of a surface of the host device. 
         FIGS. 21A-21D  illustrate an embodiment of a data input device in the form of an overlay comprising a power source for the fingerprint sensor. 
         FIG. 22  shows a flow chart illustrating an embodiment of a simple, cost effective method to enroll a fingerprint template on a device. 
         FIGS. 23A and 23B  show flow charts illustrating embodiments of a simple, cost effective method to enroll a fingerprint template on a device. 
         FIG. 24  shows a flow chart illustrating an embodiment of a simple, cost effective method to enroll a fingerprint template on a device. 
         FIGS. 25A-25D  illustrate embodiments of providing power to a smart card wirelessly. 
         FIG. 26A  illustrates an embodiment of a data input device in the form of an overlay which includes data input keys coupled to associated spatially distinct sensing areas on the sensing area of the fingerprint sensor, wherein the data input keys are remotely located from the sensing area, and a portion of the sensing area of the fingerprint sensor is exposed through a cut-out while another portion is covered by the overlay. 
         FIGS. 26B and 26C  illustrate top and bottom surfaces, respectively, of a data input device in the form of a single-layer overlay including data input keys coupled to associated spatially distinct sensing areas on a portion of the sensing area of the fingerprint sensor that is covered by the overlay and additionally including a cutout formed in the overlay to expose a portion of the sensing area of the fingerprint sensor according to some embodiments. 
         FIG. 27A  illustrates an embodiment of arranging conductive material over the sensing area of the fingerprint sensor. 
         FIG. 27B  illustrates an embodiment of arranging conductive material over the sensing area of the fingerprint sensor including activation traces on a portion of the sensing area connected to data keys and reference traces disposed between and adjacent the activation traces. 
         FIG. 28  illustrates a data input device in the form of a single-layer overlay temporarily placed over a smart card according to some embodiments. 
         FIGS. 29A and 29B  illustrate devices containing fingerprint sensors with data input keys incorporated into the device according to some embodiments. 
         FIGS. 30-31  show flow charts illustrating embodiments of an enrollment process employing a data input device in the form of an overlay in which a portion of the sensing area of the fingerprint sensor is exposed to the user through a cutout formed in the overlay. 
         FIGS. 32-33  show flow charts illustrating embodiments of an enrollment process on a device where data input keys and at least a portion of the fingerprint sensor are permanently available to the user. 
         FIG. 34A  is a plan view of a data input device in the form of an overlay integrating a power source with a host device disposed beneath the overlay according to some embodiments. 
         FIG. 34B  is a view of the data input device and host device with a portion of the overlay folded over to complete a power circuit to the host device according to some embodiments. 
         FIG. 34C  is a plan view illustrating a surface of the data input device that is placed in contact with the smart card according to some embodiments. 
         FIG. 34D  is a plan view illustrating a card placed on the data input device according to some embodiments. 
         FIG. 34E  is a plan view of an upper surface of the data input device according to some embodiments. 
         FIG. 34F  is a plan view of an overlay providing a power source to an electronic host device disposed beneath the overlay according to some embodiments. 
         FIG. 35  is a plan view of an overlay providing a power source to an electronic host device disposed beneath the overlay according to some embodiments. 
         FIGS. 36-37  show flow charts illustrating embodiments of an enrollment process on a device. 
         FIG. 38  is a top perspective view of a host device having a fingerprint sensor and a removable finger guide disposed of thereon according to some embodiments. 
         FIG. 39  is a top perspective view of the finger guide according to some embodiments. 
         FIG. 40  is a top perspective view of the finger guide with directional finger placement arrows superimposed thereon according to some embodiments. 
         FIG. 41  is a top perspective view of a finger guide disposed on a host device (e.g., smartcard) according to some embodiments. 
         FIG. 42  is a bottom perspective view of a card holder frame of a power source/finger guide according to some embodiments. 
         FIG. 43  is a top perspective view of the cardholder frame shown in  FIG. 42 . 
         FIG. 44  is a bottom plan view of the power source/finger guide of  FIG. 42  with a smart card inserted therein. 
         FIG. 45  is a top plan view of the power source/finger guide of  FIG. 44  with a smart card inserted therein. 
         FIGS. 46A-46B  is a top plan view and a partial perspective view, respectively, of an embodiment of a power source/finger guide. 
         FIGS. 47A-47F  illustrate an embodiment of a finger guide incorporated into a data input device in the form of an overlay comprising a power source. 
         FIGS. 47G-47H  illustrate an embodiment of a finger guide incorporated into an overlay comprising a power source. 
         FIGS. 47I-47L  illustrate an embodiment of a finger guide comprising a slide switch. 
         FIGS. 48A and 48B  are right and left partial perspective views of an embodiment of a finger guide. 
         FIGS. 49A, 49B, and 49C  show a user grasping a smart card with a fingerprint sensor and sensor guide using different channels of the finger guide according to some embodiments. 
         FIG. 50  schematically shows verification template images generated during an enrollment according to some embodiments. 
         FIG. 51  schematically shows verification template images generated during a two-dimensional enrollment according to some embodiments. 
         FIG. 52  schematically shows verification template images generated during a three-dimensional enrollment according to some embodiments. 
         FIG. 53A  is a top plan view of a finger guide according to some embodiments. 
         FIG. 53B  shows a close up of a retaining pins and teeth between a linearly moveable panel and fixed guide rails of the finger guide shown in  FIG. 53A . 
         FIG. 54  is a top plan view of a finger guide whereby two or more cut outs and associated finger guide channels are rotatably moveable with respect to the sensing surface to selectively align the cut out with the sensing surface and place the associated finger guide channel in operative proximity to the sensing surface according to some embodiments. 
         FIG. 55  is a top plan view of a base of a rotatable finger guide according to some embodiments. 
         FIG. 56  is a top plan view of a top part of a rotatable finger guide according to some embodiments. 
         FIG. 57  is a side view of a position selector of a rotatable finger guide according to some embodiments. 
         FIG. 58  shows a flowchart illustrating an embodiment of a method to enroll a biometric template. 
         FIG. 59  shows a flow chart further illustrating the embodiment of the method to enroll the biometric template shown in  FIG. 48 . 
         FIGS. 60A, 60B, 60C, 60D  show schematic illustrations of various embodiments of angled channels. 
         FIGS. 61A, 61B, 61C  show example profiles in cross-section of a raised section of a finger guide to illustrate how an elevation angle is achieved when the finger is tipped up by hitting the highest edge of the raised section nearest the sensing area according to some embodiments. 
         FIGS. 62A, 62B, and 62C  show schematic illustrations of finger contact with a fingerprint sensor using the fingerprint guide of  FIGS. 48A and 48B  according to some embodiments. 
         FIG. 63  shows a flow chart illustrating an embodiment of a process to re-enroll a biometric sensor, such as a fingerprint sensor, based on a trigger event the causes the sensor to go into re-enrollment mode. 
         FIG. 64  shows a flow chart illustrating an embodiment of a process for enrolling a fingerprint template in a fingerprint sensor-enabled smart card, whereby after an enrollment process, determination is made as to whether a repeat enrollment procedure should be performed for a different finger. 
         FIG. 65  shows a top perspective view of a power source according to one embodiment. 
         FIG. 66  shows a bottom perspective view of a power source according to one embodiment. 
         FIG. 67  shows a top view of one or more components of a power source according to one embodiment. 
         FIG. 68  shows a power source and a smart card according to one embodiment. 
         FIG. 69  is a table showing a list of indications according to one embodiment. 
         FIG. 70  shows a power source and smart card with status indicator lights on the smart card visible through an opening in a receptacle of the power source and arrows associating a status indicator light on the smart card with a finger guide channel on the power source receptacle. 
         FIG. 71  shows a power source and smart card with status indicator lights on the smart card and light pipes in a receptacle of the power source that direct light from the indicator lights to display windows on the power source receptacle adjacent finger guide channels on the power source receptacle. 
         FIGS. 72A-C  show a power source and smart card with status indicator lights on the smart card and photo detectors in a receptacle of the power source that are connected to indicator lights on the power source receptacle adjacent finger guide channels on the power source receptacle. 
         FIG. 73  illustrates a two finger enrollment process according to some embodiments. 
         FIG. 74  is a table showing a list of indications according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     While aspects of the subject matter of the present disclosure may be embodied in a variety of forms, the following description and accompanying drawings are merely intended to disclose some of these forms as specific examples of the subject matter. Accordingly, the subject matter of this disclosure is not intended to be limited to the forms or embodiments so described and illustrated. 
     Unless defined otherwise, all terms of art, notations and other technical terms or terminology used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. All patents, applications, published applications and other publications referred to herein are incorporated by reference in their entirety. If a definition set forth in this section is contrary to or otherwise inconsistent with a definition set forth in the patents, applications, published applications, and other publications that are herein incorporated by reference, the definition set forth in this section prevails over the definition that is incorporated herein by reference. 
     Unless otherwise indicated or the context suggests otherwise, as used herein, “a” or “an” means “at least one” or “one or more.” 
     This description may use relative spatial and/or orientation terms in describing the position and/or orientation of a component, apparatus, location, feature, or a portion thereof. Unless specifically stated, or otherwise dictated by the context of the description, such terms, including, without limitation, top, bottom, above, below, under, on top of, upper, lower, left of, right of, in front of, behind, next to, adjacent, between, horizontal, vertical, diagonal, longitudinal, transverse, radial, axial, etc., are used for convenience in referring to such component, apparatus, location, feature, or a portion thereof in the drawings and are not intended to be limiting. 
     Furthermore, unless otherwise stated, any specific dimensions mentioned in this description are merely representative of an exemplary implementation of a device embodying aspects of the disclosure and are not intended to be limiting. 
     As used herein, the term “adjacent” refers to being near or adjoining. Adjacent objects can be spaced apart from one another or can be in actual or direct contact with one another. In some instances, adjacent objects can be coupled to one another or can be formed integrally with one another. 
     As used herein, the terms “substantially” and “substantial” refer to a considerable degree or extent. When used in conjunction with, for example, an event, circumstance, characteristic, or property, the terms can refer to instances in which the event, circumstance, characteristic, or property occurs precisely as well as instances in which the event, circumstance, characteristic, or property occurs to a close approximation, such as accounting for typical tolerance levels or variability of the embodiments described herein. 
     As used herein, the terms “optional” and “optionally” mean that the subsequently described, component, structure, element, event, circumstance, characteristic, property, etc. may or may not be included or occur and that the description includes instances where the component, structure, element, event, circumstance, characteristic, property, etc. is included or occurs and instances in which it is not or does not. 
     It is now common to see fingerprint sensors installed on devices such as smartphones. A fingerprint sensor installed on a smart phone can be used to verify the identity of the user. The fingerprint sensor can also be used as a data entry or a control mechanism for the smart phone. For example, the fingerprint sensor can detect a position of the finger on its surface and translate the position of the finger as an instruction to select a function of the smart phone or to navigate within menus being displayed by the smart phone. 
     As fingerprint sensors are gaining in recognition and user acceptance, fingerprint sensors are now finding use in numerous other devices such as, for example, smart cards, fitness monitors or trackers, wearable devices, domestic and industrial appliances, automotive components, and internet of things (IOT) devices. Some devices, such as smart cards and IOT devices, have limited to no user interfaces or status indicators such as screens, speakers, LEDs, and audio signals with which the device may impart information to the user. Such devices may also have limited to no user input mechanisms for receiving user input due to lack of a keyboard, switches, buttons, and levers. 
     Such devices, as well as computers, smart phones and the like, in which user-authenticating biometric sensors, such as a fingerprint sensors, are incorporated are at times generally referred to in this disclosure as “host devices,” 
     Accordingly, there is a need for a fingerprint sensor installed on a device with limited ability to provide feedback to or obtain instructions from a user (hereinafter referred to as “limited device”) wherein the fingerprint sensor provides a data entry or a control mechanism for the device. The fingerprint sensor may have a prime purpose of verifying the user&#39;s identity, but can also function as convenient way to control or enter data into the limited device. 
     In order for a biometric sensor, such as, for example, a fingerprint sensor, to operate properly, it is essential that a sufficiently detailed template (or multiple templates) of a user&#39;s biometric data (e.g., fingerprint) is detected and stored during an enrollment process. The stored template (i.e., a verification template of biometric (e.g., fingerprint) data) is used to compare with biometric image data generated by the biometric sensor (e.g., an image of a finger sensed by the fingerprint sensor) when the device is in general use. In an embodiment employing a fingerprint sensor as the biometric sensor, a user is permitted to access a device if the sensed image of the finger matches the stored fingerprint template. Accordingly, it is important to acquire and store a fingerprint template of sufficient quality. If the stored fingerprint template is not of sufficient quality, the user may experience false acceptance and rejection at a high rate. 
     While concepts described herein are applicable to various biometric sensors and associated biometric data and verification templates of biometric data, for purposes of illustration, and not for limitation, examples are frequently described herein in the context of fingerprint sensors and fingerprint data (i.e., images). 
     For an enrollment process using a fingerprint sensor with a sensing area smaller than the surface of an average finger, a template is built up from multiple images of a finger. Specifically, the user is directed to repeatedly present his or her finger on the sensing area of the fingerprint sensor until multiple images of sufficient quality are gathered to form the template. However a fingerprint sensor installed on the limited device poses difficulties throughout the enrollment process. For example, the limited feedback/input capabilities make it difficult to notify the user: (i) to begin the enrollment process, (ii) to repeatedly present his or her finger during the enrollment process, (iii) that a sufficient number of images have been gathered, and (iv) that the enrollment process is complete. 
     Furthermore, existing solutions for enrolling a fingerprint on the limited device require the user to visit a secure location at which the user will perform the enrollment procedure. For example, enrolling a fingerprint on a smart card requires the user to visit a secure location (e.g., a bank), create a template of the user&#39;s fingerprint on a separate device with the help of a trained agent, and upload the resulting template onto the smart card. This conventional method of enrolling a fingerprint on the limited device is inconvenient for the user due to the required physical visit to a secured location. Additionally, this conventional method has come under much scrutiny because it creates a security risk due to the fact that the user cannot be sure that the user&#39;s fingerprint has not been misplaced or copied during the process of enrollment at the secured location or that the fingerprint recorded by the separate device is fully erased after enrollment is completed. Furthermore, verification accuracy may be compromised if the sensor used for enrollment of the user, i.e., the sensor of a separate device, is different from the sensor later used for verification of the user, i.e., the sensor of the limited device. 
     An object of embodiments described herein is to obviate at least some of the aforementioned problems with conventional methods of enrolling a fingerprint on a limited device. Systems, devices, and methods described herein provide a cost-effective and efficient process of enrolling a user&#39;s finger onto a limited device through a fingerprint sensor installed on the device—without the need for a separate device to receive fingerprint images—which enhances the security and improves the accuracy of fingerprint matching for the limited device. 
     In the context of the present disclosure, a “sensor element” comprises an arrangement of one or more components configured to produce a signal based on a measurable parameter (e.g., capacitance, light/optics, heat/thermal, pressure, etc.), characteristics of which will vary based on the presence or absence of an object that is in local proximity to the sensor element. A fingerprint sensor will comprise an array of such sensor elements configured to produce a signal based on a portion of the surface of a finger placed on or near the fingerprint sensor. The sensitivity of each of the sensor elements of the fingerprint sensor is such that characteristics of the signal produced at each sensor element will vary based on surface features of the portion of finger placed on or near the array, and the varying characteristics of signals produced at each sensor element may be combined or otherwise processed to form a data file with an actual or virtual “image” of the fingerprint of the portion of the finger surface placed on or near the array. 
     Specific examples of such sensor elements may include, but are not restricted to, capacitive, optical, thermal, and pressure sensor elements. As an illustrative example, two types of capacitive sensor elements that may be employed in a fingerprint sensor are mutual capacitance sensor elements and self-capacitance sensor elements. An array of mutual capacitance sensor elements comprises a plurality of spaced apart drive lines and a plurality of spaced apart pickup lines arranged transversely to the drive lines and spaced from the drive lines by a dielectric material. Each intersection of the pickup lines and the drive lines constitutes a mutual capacitance sensor element configured to produce a signal indicative of a capacitance change due to the presence or absence of a portion of an object that is in local proximity to the mutual capacitance sensor element. An array of self capacitance sensor elements comprises a first plurality of spaced apart conductive lines and a second plurality of spaced apart conductive lines arranged transversely to the first plurality of spaced apart conductive lines. Each conductive line of the first and second plurality of conductive lines is configured to transmit a signal to the finger surface placed in detectable proximity and receive a resultant signal. Accordingly, each conductive line constitutes a self-capacitance sensor element configured to produce a signal indicative of a capacitance change due to the presence or absence of a portion of an object that is in local proximity to the self capacitance sensor element. 
     In addition, sensor elements contemplated herein include both silicon-based sensors in which sensor elements are formed directly on a silicon semiconductor substrate and may form a 2-dimensional array of sensing pixels and off-silicon sensors in which sensor elements are not disposed directly on a silicon semiconductor substrate (e.g., so-called off-chip sensors) but formed on a non-silicon substrate and are conductively connected to a remotely-located control element, which may be a silicon-based semiconductor chip, such as an application specific integrated circuit (ASIC). 
     While aspects of this disclosure are presented in the context of specific types of sensor elements and fingerprint sensor configurations, it should be appreciated that implementations of those aspects are not necessarily limited to a specific type of sensor elements of fingerprint sensors described herein. 
       FIG. 1  illustrates a biometric sensor assembly or a biometric sensor, such as fingerprint sensor  102 , installed on a smart card  104  according to some embodiments. In the illustrated embodiment shown in  FIG. 1 , the smart card  104  is a limited device, as described above, and the smart card  104  comprises the fingerprint sensor  102 . In some embodiments, the smart card  104  comprises the fingerprint, or other biometric, sensor  102 , processor or processing circuitry  110 , memory  112 , and contact pads  108  providing contacts for an external power source. The processing circuity  110  may be a microprocessor, microcontroller, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or any combination of components configured to perform and/or control the functions of the smart card  104 . The memory  112  may be a read-only memory (ROM) such as EPROM or EEPROM, flash, or any other storage component capable of storing executory programs and information for use by the processing circuitry  110 . The fingerprint sensor  102  may comprise sensor controlling circuitry and a sensor memory. The sensor controlling circuity may be a microprocessor, microcontroller, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or any combination of components configured to perform and/or control the functions of the fingerprint sensor  102 . The sensor memory may be a read-only memory (ROM) such as EPROM or EEPROM, flash, or any other storage component capable of storing executory programs and information for use by the processing circuitry  110 . The sensor controlling circuitry is configured to execute fingerprint sensor application programming (i.e., firmware) stored in the sensor memory. The memory  112  and the sensor memory may be the same component. The sensor controlling circuitry is coupled to or may be part of the processing circuitry  110 . The various components of the smart card  104  are appropriately coupled and the components may be used separately or in combination to perform the embodiments disclosed herein. 
     The contact pads  108  comprise one or more power transmission contacts, which may connect electrical components of the smart card  104 , such as an LED, the processing circuity  110 , memory  112 , sensor elements (e.g., the fingerprint sensor  102 ) etc., to an external power source. In some embodiments, the contact pads  108  further comprise one or more data transmission contacts that are distinct from the power transmission contacts which connect the smart card  104  to an external device configured to receive data from and/or transmit data to the smart card  104 . In this context, the data transmission contacts of the smart card  104  are the contacts that convey data transmitted to or transmitted from the smart card  104 . 
     The processing circuitry  110  and the memory  112  may comprise a secure element module. The contact pads  108  may be part of the secure element module which includes the processor  110  and memory  112 , both of which are in electrical communication with the contact pads  108 . In an exemplary embodiment, the secure element module may conform to the EMVCo® protocol commonly used on smart cards, and the contact pads  108  provide electric contacts between the card  104  and an external card reader to provide power to the processing circuitry  110  of the card and to read data from and/or write data to the memory  112 . In  FIG. 1 , contact pads  108  embody an exemplary smart card contact arrangement, known as a pinout. Contact C1, VCC, connects to a power supply. Contact C2, RST, connects to a device to receive a reset signal, used to reset the card&#39;s communications. Contact C3, CLK, connects to a device to receive a clock signal, from which data communications timing is derived. Contact C5, GND, connects to a ground (reference voltage). In various embodiments, contact C6, VPP, may, according to ISO/IEC 7816-3:1997, be designated as a programming voltage, such as an input for a higher voltage to program persistent memory (e.g., EEPROM). In other embodiments, contact C6, VPP, may, according to ISO/IEC 7816-3:2006, be designated as SPU, for either standard or proprietary use, as input and/or output. Contact C7, I/O, provides Serial input and output (half-duplex). Contacts C4 and C8, the two remaining contacts, are AUX1 and AUX2 respectively and used for USB interfaces and other uses. 
     In embodiments described herein, the contact pads  108  are only used for providing connection points via the one or more power transmission contacts, such as C1 VCC and C5 GND, to an external power source, and no data is transmitted to or from the smart card  104  during an activation or enrollment process as described herein. The smart card  104  may comprise one or more power transmission contacts for connecting the smart card  104  to a power source, without any further data transmission capability as in a secure element module. In other embodiments, the location of the fingerprint sensor  102  may be embedded into any position on the smart card  104  such that the position of the fingerprint sensor  102  is substantially separated from the contact pads  108  and allows a user to place a finger on the fingerprint sensor  102 . 
     A user can carry out various functions on the smart card  104  by placing a finger in various positions over a sensing area  106  of the fingerprint sensor  102 . The sensing area  106  comprises a two dimensional array of sensor elements. Each sensor element is a discrete sensing component which may be enabled depending on the function of the fingerprint sensor  102 . Any combination of sensor elements in the two dimensional array may be enabled depending on the function of the fingerprint sensor. While the illustrated embodiment shown in  FIG. 1  describes the fingerprint sensor  102  in relation to the smart card  104 , this is not required and the fingerprint sensor  102 , or other biometric sensor, may be incorporated in a different limited device in other embodiments. For example, other limited devices in which aspects of the technology describe herein may be incorporated include fitness monitors, wearable devices, domestic and industrial appliances, automotive components, and “internet of things” (IOT) devices. 
     In some embodiments, the sensing area  106  can have different shapes including, but not limited to, a rectangle, a circle, an oval, or a lozenge. 
     The sensor  102  may comprise an array of sensor elements comprising a plurality of conductive drive lines and overlapped conductive pickup lines that are separated from the drive lines by a dielectric layer. Each drive line may thus be capacitively coupled to an overlapping pickup line through a dielectric layer. In such embodiments, the pickup lines can form one axis (e.g., X-axis) of the array, while the drive lines form another axis (e.g., Y-axis) of the array. Each location where a drive line and a pickup line overlap may form an impedance-sensitive electrode pair whereby the overlapping portions of the drive and pickup lines form opposed plates of a capacitor separated by a dielectric layer or layers. This impedance-sensitive electrode pair may be treated as a pixel (e.g., an X-Y coordinate) at which a surface feature of the proximally located object is detected. The array or grid forms a plurality of pixels that can collectively create a map of the surface features of the proximally located object. For instance, the sensor elements forming the pixels of the grid produce signals having variations corresponding to features of a fingerprint disposed over the particular sensor element and thus the pixels along with circuity controlling the sensor elements and processing signals produced by the sensor elements that includes a processor and signal conditioning elements (i.e., “sensor controlling circuitry”) that may be incorporated into an integrated circuit can map locations where there are ridge and valley features of the finger surface touching the sensor array. 
     Additional details of a fingerprint sensor with overlapping drive lines and pickup lines as well as the drive, sense, and scanning electronics, are discussed in U.S. Pat. No. 8,421,890, entitled “Electronic imager using an impedance sensor grid array and method of making,” U.S. Pat. No. 8,866,347, entitled “Biometric sensing”, and U.S. Pat. No. 9,779,280, entitled “Fingerprint Sensor Employing an Integrated Noise Rejection Structure,” the respective disclosures of which are incorporated by reference in their entirety. Further improvements and enhancements to the devices, methods, and circuitry used to improve the sensitivity of the measurement principal employing a sensor grid comprised of overlapping drive lines and pickup lines separated by a dielectric including the drive, sense, scanning, and noise reduction electronics, are described in U.S. Pat. No. 9,779,280. 
     An exemplary installation of a fingerprint sensor in a smart card is described in U.S. Pat. No. 9,122,901, the disclosure of which is hereby incorporated by reference. 
     The sensing area  106  of the biometric sensor, (e.g., fingerprint sensor  102 ) installed on the device  104  may be selectively configured to operate in five modes: (1) enrollment mode; (2) verification mode; (3) data input mode; (4) control mode; and (5) unlock mode. The user may select the different modes by different interactions with the sensor, such as a double tap, hold, up/down drag, and left/right drag on the sensor area  106 . In other embodiments, the sensor may be selectively configured in different modes by placing a data input device over the sensing area  106 . Data input devices configured for different sensor operation modes may include unique detectable features that, when detected by the sensor, will configure the sensor in a mode corresponding to the data input device. 
     In the context of this disclosure, a “data input device” is any device that may be attached or otherwise coupled to a host device and is thereby coupled to a biometric sensor of the host device to enable a user to provide inputs to the host device through the biometric sensor via features of the data input device that allow the user to interface with the biometric sensor to provide control inputs or inputs of data in addition to the particular biometric data that the biometric sensor is configured to detect. For instance, in examples described herein, the data input device includes keys or buttons that are each uniquely coupled to a fingerprint sensor of the host device so that a user contacting any such key or button generates a unique control input or a unique data input corresponding to that key or button. In addition, in other examples described herein, the attachment or coupling of the data input device to the host device, or its removal, may itself provide data input to the host device, for example, communicating that the data input device has been attached or coupled to, or removed from, the host device, that the data input device has or has not been properly positioned with respect to the biometric sensor to enable proper control or data input by the user, or, as described above, to place the biometric sensor in one of a number of operating modes. 
     In some embodiments, when the fingerprint sensor  102  is in enrollment mode, all of the sensor elements in the two dimensional array of the sensing area  106  are activated in a fingerprint sensing mode to produce signals—such as capacitance—having detectible variations corresponding to fingerprint features—grooves and ridges—in detective proximity to the sensor array (i.e., in physical contact with the sensor elements or in sufficient proximity to the sensor elements to produce signals corresponding to fingerprint features) which together form an “image” of the fingerprint, and the sensor controlling circuitry is configured so that multiple images of a user&#39;s fingerprint may be gathered, and, possibly, manipulated, to acquire a sufficient fingerprint template that may be subsequently stored in memory. An exemplary enrollment process is described in U.S. Pat. No. 9,684,813, entitled “System and Method of Biometric Enrollment and Verification,” the disclosure of which is hereby incorporated by reference. The stored fingerprint template may be continuously updated based on the user&#39;s use of the fingerprint sensor over time. 
     In some embodiments, when the fingerprint sensor is in verification mode (also known as authentication mode), all of the sensor elements in the sensing area  106  are activated in fingerprint sensing mode and the sensor controlling circuitry is configured so that an image of the user&#39;s fingerprint may be acquired and compared with the fingerprint template stored in memory to verifying that whether the acquired fingerprint image sufficiently matches the fingerprint template. An exemplary verification process is also described in U.S. Pat. No. 9,684,813. An exemplary verification process is also described in U.S. patent application Ser. No. 15/356,989 (Publication No. U.S. 2018-0144173) entitled “Combination of Fingerprint and Device Orientation to Enhance Security,” the disclosure of which is hereby incorporated by reference. Ideally, in both the enrollment mode and the verification mode, a finger should be placed centrally on the sensing area  106  of the fingerprint sensor  102  in order to obtain the best image of the finger. 
     In some embodiments, when the fingerprint sensor is in control mode and data input mode, the sensor elements in the sensing area  106  are activated in contact sensing mode, data input keys are operatively coupled to associated spatially distinct regions or control areas of the sensing area to enable direct or indirect contact by a user&#39;s finger with each associated spatially distinct area, and the sensor controlling circuitry is configured so that the user may input data through the sensing area  106  by directly or indirectly placing a finger on selected, associated spatially distinct control areas within the sensing area  106  of the fingerprint sensor  102 . That is, as opposed to the enrollment and verification modes, in which the sensor elements and the processor of the sensor controlling circuitry are configured to detect and map different fingerprint features of the finger surface, in contact sensing mode for the control and data input modes, the sensor elements and the sensor controlling circuitry may be configured to merely detect whether or not the sensor element is directly or indirectly contacted by a finger surface and to distinguish a spatially distinct region of the sensor array in which the contacted element(s) reside. 
     In both the control mode and the data input mode, the sensing area  106  may be divided into spatially distinct control areas dedicated to a specific command or data input. The number and location of the spatially distinct control areas within the sensing area  106  may be configured depending on the desired use of the fingerprint sensor  106 , the size of the sensing area  106 , and the ability of the fingerprint sensor  102  to accurately distinguish contact by the finger with the different spatially distinct regions on the sensor. In unlock mode, the device  104  may maintain the data input mode until the user inputs a correct unlock code, wherein the input of the correct code unlocks the device  104 . 
     In some embodiments described herein, when the fingerprint sensor is in control mode and data input mode, a first portion of the sensor elements in the sensing area  106  are activated in contact sensing mode, data input keys are operatively coupled to associated spatially distinct regions or control areas of the first portion of the sensing area to enable direct or indirect contact by a user&#39;s finger with each associated spatially distinct area, and the sensor controlling circuitry is configured so that the user may input data through the sensing area  106  by directly or indirectly placing a finger on selected, associated spatially distinct control areas within the first portion of the sensing area  106  of the fingerprint sensor  102 . In such embodiments, when the fingerprint sensor is in enrollment mode, only the sensor elements located within a second portion of the two-dimensional array of the sensing area  106  different from the first portion and accessible to a user&#39;s finger may be activated in the fingerprint sensing mode and the sensor controlling circuitry is configured so that multiple images of a user&#39;s fingerprint may be gathered to acquire a sufficient fingerprint template that is stored in memory. 
       FIG. 2A  is a top view of a sensing area  106  of a fingerprint sensor  102  installed on a device with limited ability to provide feedback to or obtain instructions according to some embodiments. As shown in  FIG. 2A , the sensing area  106  includes indicia formed on the different quadrants (spatially distinct regions) of the sensing area to facilitate data input. In verification or enrollment mode, the user may place a finger on the center of the sensing area  106  to produce a fingerprint image. When the fingerprint sensor  102  is used in data input mode, each spatially distinct region can function as a data input “key”, and the user can enter numbers (e.g., an activation code, such as a PIN code) by tapping his or her finger on the numbered regions or areas  202 A-D of the sensing area  106 . As shown in  FIG. 2A , the sensing area  106  can be divided into four separate spatially distinct control areas  202 A-D. In the illustrated embodiment shown in  FIG. 2A , the user may place a finger on the top left quadrant  202 A, numbered 1, of the sensing area  106 . Accordingly, the sensor elements located in the top left quadrant  202 A of the sensing area  106  may sense contact by the finger and the fingerprint sensor  102  may determine the location of the transmitting sensor elements and process the received signals to be an input by the user representing the number “1.” In the embodiment shown in  FIG. 2A , the user may place a finger on different quadrants  202 A-D to input the number 1, 2, 3, and 4 in any sequence. In another embodiment, the sensing area  106  may be divided into more or less spatially distinct control areas. For example, there may be 6 spatially distinct control areas representing numbers 1-6 or two control areas representing numbers 1 and 2 (or letters A and B). Accordingly, the user is able to input numbers corresponding to the spatially distinct keys of the sensor array in any sequence through the sensing area. In another embodiment, all or part of the sensing area  106  may be employed as a single spatially distinct control area dedicated to a Morse code-type input by the user (e.g., sequentially-repeated, separate contacts with the same spatially distinct control area, each contact of a different, specified duration). The one spatially distinct control area may be positioned in any portion of the sensing area  106  or comprise the entire sensing area  106 . In another embodiment, any kind of alphabetical characters, symbols or instructions (e.g., instructions for the device to attempt to connect to WiFi via WPS, disconnect/reconnect WIFI, change operating mode, pair with Bluetooth, etc.), or combination of these could be entered in a similar way depending on the desired operating function. 
     In some embodiments, the sensing area  106  may be large enough so that each spatially distinct control area  202 A-D can sense an entire finger. Accordingly, each spatially distinct control area  202 A-D may independently verify a finger and be used to give authentication to access a device. For example, a key fob that can start  1  of 2 or more automobiles for a verified user may implement such spatially distinct control areas on its sensing area. That is, a universal key fob configured to lock/unlock and start an automobile may include a fingerprint sensor large enough to accommodate 2, 3, 4, or more specifically distinct regions each large enough to image enough of a fingerprint for verification. Each distinct region of the key fob can be configured so that activation of the region corresponds to a different automobile. Thus, the key fob can be configured to permit an authorized user to operate any of 2, 3, 4, or more automobiles by touching a specific region of the sensor corresponding to a particular vehicle and providing a verifying fingerprint. 
       FIG. 2B  is a top view of the sensing area  106  of the fingerprint sensor  102  in control mode according to some embodiments. In verification or enrollment mode, the user may place a finger on the center of the sensing area  106  to produce a fingerprint image. In control mode, the user may control a device by placing a finger on spatially distinct control areas within the sensing area  106  of the fingerprint sensor  102 . In the illustrated embodiment shown in  FIG. 2B , the fingerprint sensor  102  is installed on a wearable fitness monitor. In control mode, the user may pause or start the monitoring by placing his or her finger on the appropriate quadrant  202 A-D of the sensing area  106  during normal operation of the wearable fitness monitor. As shown in  FIG. 2B , the top left quadrant  202 A of the sensing area  106  is marked with a “pause” symbol, and the bottom right quadrant  202 D of the sensing area  106  is marked with a “play” symbol. Accordingly, the user can pause the monitoring by placing a finger on the top left quadrant  202 A and start/resume the monitoring by placing a finger on the bottom right quadrant  202 D. 
     In some embodiments, regions  202 B and  202 D may be non-functional, reserved for other manufacturer-defined functions, or reserved for certain user-defined functions. 
     As shown in  FIGS. 2A-2B , the spatially distinct control areas may be visible to the user. In some embodiments, the dividing lines  204 A-B (“cross hairs”) may be indicated on the sensing area  106  and visible to the user continually during operation of the fingerprint sensor  102 . In other embodiments, an elliptical shape  206  may be indicated on the sensing area  106 . In such embodiments, the elliptical shape  206  is centered in the sensing area  106  to encourage the user to place a finger centrally on the sensing area  106  when using the fingerprint sensor  102  in enrollment or verification mode. Different shapes may be used for the indication instead of the elliptical shape  206 . The indication of the dividing lines  204 A-B and the elliptical shape  206  may be implemented by the use of distinguishing colors, lines, and textures achieved through printing and/or etching. A suitably chosen overlay which does not adversely impact the sensitivity of the sensing area  106  may be used to indicate the spatially distinct control areas. 
     In some embodiments, an OLED display may operate as the fingerprint sensor  102 . In such embodiments, the fingerprint sensor  102  may display the indication of the dividing lines  204 A-B and the elliptical shape via the OLED display. Exemplary embodiments of the OLED display configured to operate as a fingerprint sensor are described in U.S. Patent Application Publication No. US 2017-0308228, entitled “Display with Integrated Touch Screen and Fingerprint Sensor,” the disclosure of which is incorporated by reference in its entirety. 
       FIGS. 3A-3B  illustrate an application of a data input device in the form of an overlay  302  placed over the sensing area  106  of the fingerprint sensor  102  installed on a smart card  104  according to some embodiments. As shown in  FIGS. 3A-3B , the overlay  302  may be placed over the sensing area  106  of the fingerprint sensor  102  of the smart card shown in  FIG. 3A . A battery or external power source may be connected to one or more of the contact pads  108  to provide power for the operation of the fingerprint sensor  102 . The overlay  302  may comprise an adhesively-backed sticker or film temporarily and removably placed over a portion of the card  104  including the sensing area  106  of the fingerprint sensor  102 , as shown in  FIG. 3B . Repositionable adhesives provided by companies such as 3M, Krylon, Franklin Adhesives and Polymers, and Bostik may be applied to the overlay  302  to temporarily place over the portion of the card  104  including the sensing area  106 . The overlay  302  may indicate the spatially distinct control areas of the sensing area  106  through pierced holes  304 A-D defining four data input keys, each being associated with a spatially distinct control area of the sensing area  106 . The pierced holes  304 A-D may provide a zoning effect without impacting the sensitivity of the fingerprint sensor  102 . As shown in  FIG. 3B , the four pierced holes  304 A-D indicate the spatially distinct control areas on the sensing area  106  of the fingerprint sensor  102  corresponding to numbered “keys” 1, 2, 3, and 4. In other embodiments, there may be a larger number or smaller number of pierced holes depending on the function of the fingerprint sensor. The user may input a numerical activation code (also referred to as an authentication code) by placing a finger over the spatially distinct control areas in a sequence according to the activation code, thus unlocking and putting the smart card  104  into the enrollment mode. Instructions may be provided on the overlay  302  to give guidance to the user, and each spatially distinct control area may be labeled or numbered. For example, the user may call a phone number listed on the overlay  302 , such as, a 1-800 phone number, to retrieve the numerical activation code to be entered or the user may receive an SMS text on their personal cell phone from a secure financial institution. Once the user retrieves the numerical activation code, the user may input the code by connecting the card  104  to a power source and placing a finger over the numbered spatially distinct control areas in a sequence according to the code, thus unlocking the card. Accordingly, only authorized end users may unlock a locked card  104  delivered through a public mail system. A user may input a gesture over the sensing area  106 , such as swiping a pattern to join a plurality of spatially distinct control areas in a predetermined sequence. 
     The overlay  302  may comprise a single pierced hole defining one data input key, the one data input key being associated with a spatially distinct control area of the sensing area  106  configured to receive a Morse code-type data input by the user. In such embodiments, the user may retrieve activation instruction and input the activation code according to the retrieved instruction by making one or more separate sequential contacts of varying, specified durations with the input key. For example, the user may call a specified phone number to be instructed to use a finger to press down on the data input key when the user hears a beep and to lift the finger when the beep ends. This process could be repeated for one or more additional beeps of varying durations. The user may receive the Morse code activation instructions through an SMS text or a downloadable audio file. 
     In some embodiments, contact with the sensor may be determined by the fingerprint sensor  102  and sensor controlling circuitry by scanning the entire sensing area  106 , cancelling any background noise, and calculating an average measurement at each sensor element in order to determine a signal exceeding a threshold indicating contact with the sensor element. If sensor elements registering a signal exceeding the threshold are confined to one discrete spatially distinct region—meaning the user has touched only one “key”—the contact is registered as a valid input—not necessarily the “correct” input, which is determined by the sequence provided by the code, but merely that a valid input was received. If sensor elements registering a signal exceeding the threshold are not confined to one discrete spatially distinct region—meaning the user has simultaneously touched more than one key—the contact is registered as an error. The system can be configured to register multiple touches as a valid input to increase the number of possible inputs from which a unique activation code can be constructed. For example, while contact with the “1” key and the “2” key constitute two valid possible inputs, simultaneous contact with both the “1” key and the “2” key may constitute a third valid possible input. 
     The fingerprint sensor  102  may detect an absence of a finger placed over the sensing area  106 —i.e., absence of a signal—to distinguish between each data input by the user. 
     After the activation code has been successfully entered, the overlay  302  may be peeled off and disposed of when no longer used. In some embodiments, a small tab  310  sticks out of one side or corner of the overlay  302  so that the user may peel off the overlay  302  with ease. Care should be taken, however, to ensure that the card is not unintentionally removed from the power source in the process of peeling the overlay  302  off the card  104 . The small tab  310  may be located on an edge or corner of the overlay  302  which encourages the user to peel off the overlay  302  in a direction moving towards the power source, rather than pulling away from the power source, to avoid dislodging the card from the power source. 
     As shown in  FIG. 3B , the card  104  may include an LED  308  or other indicator element, and the overlay  302  may comprise a pierced hole  306  positioned over the LED  308  allowing the user to see the LED when the overlay  302  is temporarily placed over a portion of the card  104  including the sensing area  106  and the LED  308 . The LED  308  may illuminate and flash to communicate various instructions and confirmations to the user. For example, the LED may show: (1) a solid light for 2-3 seconds which indicates that the fingerprint sensor  102  is powering up when the card  104  is properly connected to a power source; (2) a single flash that indicates that a valid entry by the user has been made; (3) short repeated flashes that indicate that an entry made by the user has not been made (i.e., an invalid entry attempt); (4) solid light for a long period of time, e.g., 5 seconds, which indicates that a code or data entry made by the user is correct; (5) long repeated fast flashes which indicates that a code or data entry made the user is incorrect; and (6) rapid repeated flashes when the user has exhausted a maximum number of input attempts without correctly entering the activation code. In another embodiment, the LED  308  may be multicolor. Accordingly, the LED  308  may flash different colors in a variety of combinations to communicate the various instructions and confirmations described above. 
     In some embodiments, the card  104  may include more than one LED  308  or other indicator element. In such embodiments, more than one LED  308  may flash different colors to communicate the various instructions and confirmations described above. For example, when there is one red LED and one green LED, the following states may be indicated: (1) both LEDS are off until power is applied to the card; (2) when power is applied, if a fingerprint template is already enrolled on the card, the green LED is on solid; (3) if no fingerprint template is enrolled on the card, an enrollment sequence starts described by the following steps 4 to 10; (4) the green LED flashes until a finger is placed on the sensor, or until a finger that remains on the sensor since the previous image capture step is taken off the sensor and then put back down again; (5) the green LED goes off when the finger is on the sensor and an image is captured; (6) if the detected sensor coverage by the finger is less than a threshold denoting a poor image capture, the red LED goes on solid for 1 second and the sequence returns to step (4); (7) if the detected sensor coverage is more than or equal to a threshold denoting likelihood of a good image capture, both LEDs stay off while the captured image is assessed to determine if it should be enrolled; (8) if the image is enrolled, the green LED goes on solid for one second, otherwise if the image has not been enrolled, the red LED goes on solid for one second; (9) repeat steps 4 to 8 until a sufficient fingerprint template is created; (10) the green LED goes on solid to indicate the process has completed successfully. The enrollment sequence (also referred to as the enrollment mode) may be terminated after the fingerprint template is stored. A flexible display such as an OLED may be embedded into the body of the card  104  to provide the user with detailed visual and textual feedback. 
     The fingerprint sensor  102  may include a screen or a sound emitting unit, such as an audio speaker or a vibrator, to provide feedback to the user such as a status indication. In such embodiments, the overlay  302  may be shaped or contain a cutout so the user may observe the screen and receive the status indication. In some embodiments, an OLED display may operate as the fingerprint sensor. In such embodiments, the fingerprint sensor  102  may provide feedback to the user such as a status indication via the OLED display. 
       FIGS. 4A-4C  are top plan views of a data input device in the form of an overlay  402  temporarily placed over the sensing area  106  with different configurations of pierced holes  404 A-D formed in the overlay  402  according to some embodiments. As shown in  FIGS. 4A-4C , the pierced holes  404 A-D are defined spaces, such as holes or windows, in the overlay  402  surrounded by material. The surrounding material prevents a finger from making contact with the underlying sensing area  106  when a finger is placed on the overlay  402 . The pierced holes  404 A-D may be in a circle, oval, square or polygon shape. The pierced holes  404 A-D may define data input keys associated with spatially distinct control regions of the sensing area  106  used to input data or otherwise control a device in which the fingerprint sensor  102  is installed. In the embodiments illustrated in  FIGS. 4A-4C , only a portion of each pierced hole  404 A-D overlies a portion of the sensing area  106 , and the spatially distinct regions of the sensing area corresponding to the pierced holes  404 A-D do not collectively constitute the entire sensing area  106 . Technically, a spatially distinct region may be defined by a single sensor element (pixel) so long as the data input device (e.g., overlay) is configured so that a user contact with a particular “key” of the data input device corresponding to the spatially distinct region is detected at that single sensor element. This allows the fingerprint sensor area  106  and the overlay  402  to provide a larger effective touch entry area (as shown by the dotted lines  405  in  FIG. 4A ) for the user while maintaining accurate finger detection. 
       FIG. 4A  illustrates an embodiment of the pierced holes  404 A-D in which the pierced holes  404 A-D are shaped as circles and located at each corner of the sensing area  106 . As shown in  FIG. 4A , each of the pierced holes  404 A-D defines a circle sector sensing area  406 A-D for each associated spatially distinct control area. The circle sector sensing areas  406 A-D are responsible for detecting a finger when placed over the corresponding hole  404 A-D. In some embodiments, the pierced holes  404 A-D are separated at an optimal distance so that the fingerprint sensor  102  may distinguish which spatially distinct control area of the sensing area  106  a user is touching while maintaining the largest area for each circle sector sensing area  406 A-D. As described above, in an embodiment, the fingerprint sensor  102  may recognize and reject any data input when the user simultaneously places a finger over two or more spatially distinct control areas of the sensing area  106 . In some embodiments, 8 mm diameter circles may be used for the pierced holes  404 A-D. 
     The fingerprint sensor  102  may not scan for every sensor element in the two dimensional array of sensor elements in the sensing area  106 , which may improve sensor response time in data input mode. For example, the fingerprint sensor  102  may scan every sensor element in the sensing area  106  not covered by the overlay  402 . As shown in  FIG. 4A , the fingerprint sensor  102  may recognize the exposed sensing areas defined by the circle sector sensing areas  406 A-D. Accordingly, the fingerprint sensor  102  may scan the sensor elements located within the circle sector sensing areas  406 A-D. 
     In some embodiments, since the sensor  102  does not require the same resolution in a data input mode as is required in a fingerprint sensing mode, the fingerprint sensor  102  may scan for every other, or every third (or more) sensor element in a row or a column of the two dimensional array of sensor elements in the sensing area  106  (or in the sensing areas  406 A-D), which may improve sensor response time in data input mode. 
     In some embodiments, each pierced hole  404 A-D may be placed at the edge of each corner of the sensing area  106  so that each circle sector sensing area  406 A-D is reduced to one sensor element, which may improve the distinction between each spatially distinct control area of the sensing area  106 . In such embodiments, each spatially distinct control area of the sensing area  106  comprises one sensor element responsible for detecting a finger when placed over the corresponding hole  404 A-D. 
       FIG. 4B  illustrates another embodiment of the pierced holes  404 A-D. As shown in  FIG. 4B , the pierced holes  404 A-D are shaped as squares with rounded corners and located at each corner of the sensing area  106 . Accordingly, each of the pierced holes  404 A-D forms a square sensing area with a round corner  408 A-D. The rounded square configuration of the pierced holes  404 A-D allows for a larger portion of the sensing area  106  to be dedicated to each associated spatially distinct control area compared to the circle configuration. The rounded squares may each comprise a length and width of 8 mm, for example. 
     The fingerprint sensor  102  may scan only the sensor elements located within the sensing areas  408 A-D and may scan for every other, or every third (or more) sensor element in a row or a column of the two dimensional array of sensor elements in the sensing area  106  (or in the sensing areas  408 A-D), which may improve sensor response time in data input mode. 
     In some embodiments, each pierced hole  404 A-D may be placed at the edge of each corner of the sensing area  106  so that each square sensing area with a round corner  408 A-D is reduced to one sensor element, which may improve the distinction between each spatially distinct control area of the sensing area  106 . In such embodiments, each spatially distinct control area of the sensing area  106  comprises one sensor element responsible for detecting a finger when placed over the corresponding hole  404 A-D. 
       FIG. 4C  illustrates another embodiment of the pierced holes  404 A-D. As shown in  FIG. 4C , the pierced holes  404 A-D are shaped as circles and located at each side of the sensing area  106 —as opposed to each corner. Accordingly, each of the pierced holes  404 A-D forms a circle segment sensing area  410 A-D at each side of the sensing area  106 . The configuration of the pierced holes  404 A-D shown in  FIG. 4C  has the advantage of providing a large sensing area for each spatially distinct control area, while providing a minimal distance in between each of the distinct control areas. 
     In some embodiments, the fingerprint sensor  102  scans only the sensor elements located within the sensing areas  410 A-D and may scan for every other, or every third (or more) sensor element in a row or a column of the two dimensional array of sensor elements in the sensing area  106  (or in the sensing areas  410 A-D), which may improve sensor response time in data input mode. 
     In some embodiments, each pierced hole  404 A-D may be placed at the edge of each side of the sensing area  106  so that each circle segment sensing area  410 A-D is reduced to one sensor element, which may improve the distinction between each spatially distinct control area of the sensing area  106 . In such embodiments, each spatially distinct control area of the sensing area  106  comprises one sensor element responsible for detecting a finger when placed over the corresponding hole  404 A-D. 
       FIGS. 5A-5B  shows a data input device in the form of a frame  502  used in relation with the sensing area  106  according to some embodiments. As shown in  FIGS. 5A-5B , a frame  502  with pierced holes  506 A-B may be aligned with the fingerprint sensor  102 . The number, shape, and size of the pierced holes  506 A-B may differ as described above in relation to  FIGS. 4A-4C . As shown in  FIG. 5A , the frame  502  may be positioned on the fingerprint sensor  102  with a hinge allowing the frame  502  to flip open and reveal the entire sensing area  106  for fingerprint sensing. As shown in  FIG. 5B , the frame  502  may be flipped down to indicate the spatially distinct control areas  504 A-B wherein the spatially distinct control areas  504 A-B depend on the sensing area  106  revealed through the pierced holes  506 A-B in the frame  502 . The frame  502  may be positioned on the device that contains the fingerprint sensor  102 . In such embodiments, the frame  502  is appropriately positioned on the device such that the frame  502  covers the sensing area  106  when flipped down and indicates the spatially distinct control areas as shown in  FIG. 5B . The frame  502  may enable a user to control the device that contains the fingerprint sensor  102  by placing a finger on the spatially distinct control areas  504 A-B. For example, the user may place a finger on a wireless protected setup (WPS) key  504 A to connect the device to WiFi or place a finger on a reset key  504 B to reset the device. In other embodiments, frame  502  may be positioned on the fingerprint sensor or the device that contains the fingerprint sensor with a slider such that the frame  502  may slide back and forth in direction “A” to conceal or reveal the sensing area  106 . 
     In some embodiments, a detectable feature of the frame  502  can be sensed by one or more sensor elements of the sensing area  106  to determine that the frame  502  is flipped down and to put the sensor area  106  in data input mode to detect contact with one of the spatially distinct keys  504 A or  504 B. The detectable feature may be a metal, metalized paint or conductive ink, conductive polymer or any conductive coating added to the side (bottom) of the frame  502  that comes in contact with the sensing area  106  when the frame  502  is flipped shut. In such embodiments, the metal, metalized paint, conductive ink, conductive polymer, or any conductive coating allows the fingerprint sensor  102  to detect whether the frame  502  is open or closed. The fingerprint sensor  102  may switch modes depending on whether the frame  502  is open or closed. For example, when the frame  502  is open and the entire sensing area  106  is revealed, the fingerprint sensor  102  no longer detects the metal, metalized paint or conductive ink and enters a fingerprint sensing mode, such as, for example, the verification mode or the enrollment mode. As another example, when the frame  502  is closed, the fingerprint sensor  102  detects the metal, metalized paint or conductive ink and enters a mode depending on the configuration of the metal, metalized paint or conductive ink. In some embodiments, conductive ink may be added to the bottom of the frame  502  according to a predetermined pattern such that the fingerprint sensor  102  may detect and recognize the pattern and enter a particular mode based on the pattern. The frame  502  may comprise one or more metalized dome switches which provide tactile feedback to the user. In such embodiments, an input by the user is detected by the sensing area  106  when finger pressure is applied to a surface of the dome switches. For example, the one or more metalized dome switches may look like the typical keypad on a microwave oven. 
     A frame may include more than one flipable data input device, each providing a distinct functionality. Each data input device may be provided with a different detectable feature—e.g., a conductive ink applied in a unique pattern—to be detected by the sensor and to configure the sensor in a different data input mode corresponding to the specific data input device. 
       FIGS. 6A-6C  illustrate the use of a data input device in the form of a double layered overlay  602  which may be temporarily placed over the sensing area  106  according to some embodiments. As shown in  FIGS. 6A-6C , the double layered overlay  602  comprises an upper layer  604  and a lower layer  606 , wherein the bottom of the lower layer  606  contacts the surface of the sensing area  106  when the double layered overlay  602  is placed over the sensing area  106 . As shown in  FIG. 6B , the upper layer  604  comprises one or more pierced holes  608 A-D. The surface of the edge surrounding each pierced hole  608 A-D may be slightly raised such that a user may feel the circumference of the hole when placing a finger over it. As shown in  FIG. 6C , the lower layer  606  is not pierced and is made of a thin continuous sheet of material according to some embodiments. The surface of the lower layer  606  may be colored or include printed indicia, a textured pattern, or a design aligned with the pierced holes  608 A-D to indicate the spatially distinct control areas to the user. The material of the lower layer  606  may be a thin polymer, typically no more than 50-100 microns in thickness. The material and thickness of the lower layer  606  should be such as to not negatively impact the detection of contact with the sensing area through the pierced holes  608 A-D. 
     As shown in  FIG. 6C , numbers or other indicia may be printed on the surface of the lower layer  606 . The position of the numbered portions  610 A-D on the surface of the lower layer  606  corresponds to the position of the pierced holes  608 A-D on the upper layer  604 . Accordingly, when the upper layer  604  and the lower layer  606  are combined to form the double layered overlay  602 , the numbered portions  610 A-D indicate the location of the spatially distinct control areas through the pierced holes  608 A-D of the upper layer  604 . The indicia may be printed on the upper layer  604 . In such embodiments, the indicia may be printed substantially close to the pierced holes  608 A-D so that a user may associate a separate indication for each pierced hole  608 A-D. 
       FIG. 7A  illustrates an embodiment of a data input device in the form of an overlay  702  with complex piercing patterns used in relation with the sensing area  106  of the fingerprint sensor  102 . The overlay  702  with piercing arranged in detectable patterns, i.e., piercing patterns  704 , may be used to provide a further security mechanism for the fingerprint sensor  102 . For example, the patterned overlay  702  may be issued to a user and temporarily placed over the sensing area  106  to be used like a stencil for a “quick response” or QR® code (or other 2D detectable code), wherein the complex piercing pattern may constitute a unique pattern associated with the user or the device which contains the fingerprint sensor. The overlay  702  and the device on which the fingerprint sensor  102  is installed may be issued. When the user places a finger  701  over the complex piercing patterned overlay  702 , preferably contacting all the piercings  704  simultaneously, the fingerprint sensor  102  only detects contact with portions of the sensing area  106  exposed through the complex pattern of piercings  704 . Accordingly, the complex piercing patterned overlay  702  may function as an access code or “key” to access or otherwise utilize functions of the device on which the fingerprint sensor  102  is installed. For example, touching the sensing area  106  through the complex piercing patterned overlay  702  could put the device into a particular operating mode, or unlock special functionalities such as putting the fingerprint sensor  102  into the “enroll” mode, or performing a factory reset of the device. 
     The complex piercing patterns  704  on the overlay  702  may be converted into a digital representation that is stored in the memory of the device. In such embodiments, the device may require the user to touch the sensing area  106  through the complex piercing patterned overlay  702  in order to initiate a fingerprint enrollment process. For example, when the user places a finger  701  over the complex piercing patterned overlay  702 , the fingerprint sensor  102  may detect the finger  701  through the complex piercing pattern  704  and compare the detected image with the stored digital representation of the complex piercing pattern  704 . In some embodiments, if the detected image does not match the stored digital representation of the complex piercing pattern, the device could shut off to prevent further access by the user or emit a warning. Depending on the level of security required, the degree of matching that indicates “success” or “failure” could be made more or less strict. 
     Another application of the complex piercing patterned overlay  702  is to deter piracy or tampering of products. In some embodiments, devices may be sold with the complex piercing patterned overlay  702  placed over the sensing area  106 . In such embodiments, the devices may only be enabled for the first time when a user places a finger over the sensing area  106  through the complex piercing patterned overlay  702 , thus assuring the user that the product is genuine and/or has not been tampered with. In the embodiments disclosed in relation to  FIG. 7A , the complex piercing patterned overlay  702  is used in combination with the finger  701  touching a fingerprint sensor  102 . However, the concept of the complex piercing pattern  704  may by applied generally to any biometric sensor, e.g., iris, retina, palm printing, or to any device with a touchscreen in alternative embodiments. 
       FIG. 7B  illustrates a data input device in the form of an overlay  706  with printed patterns  708  used in relation with the sensing area  106  of the fingerprint sensor  102  according to some embodiments. In such embodiments, the overlay  706  comprises a pattern  708  of conductive material printed on it. The pattern  708  may be arranged in detectable patterns and may be used to provide a further security mechanism for the fingerprint sensor  102 . 
     For example, the patterned overlay  706  may be issued to a user and temporarily placed on top of the sensing area  106  to be used like a “quick response” or QR® code (or other 2D detectable code), wherein the printed pattern  708  may constitute a unique pattern associated with the user or the device which contains the fingerprint sensor. The overlay and the device on which the sensor is installed may be issued separately. When the patterned overlay  706  is placed on top of the sensing area  106  of the fingerprint sensor  102  the printed pattern  708  comes in contact with the surface of the sensing area  106 , and sensor elements of the fingerprint sensor  102  spatially corresponding to elements of the pattern  708  detect contact with the printed pattern  708 . Accordingly, the printed patterned overlay  706  may function as an access code or “key” to access or otherwise utilize functions of the device on which the fingerprint sensor  102  is installed. For example, putting the sensing area  106  in contact with the printed patterned overlay  708  may put the device into a particular operating mode or unlock special functionalities, such as putting the fingerprint sensor  102  into “enroll” mode, or performing a factory reset of the device. 
       FIG. 8  illustrates a method of calibration for the fingerprint sensor  102  according to some embodiments. In some instances, a data input device such as an overlay or frame, as described in  FIGS. 3-7 , may be misaligned with the sensing area  106 . In the illustrated embodiment shown in  FIG. 8 , an a data input device in the form of an overlay  802  is temporarily placed over the sensing area  106  wherein the overlay  802  is misaligned with the sensing area  106 . The overlay  802  may comprise detectable features and the location of such features as detected by the sensor  102  may indicate the position of the overlay  802  with respect to the sensing area  106 . For example, a vertical conductive line  804 A and a horizontal conductive line  804 B may be applied (e.g., with conductive ink) to the back surface of the overlay  802  to form “cross-hairs” at the center of the overlay  802 . The fingerprint sensor  102  may be configured to expect the conductive lines  804 A-B to be placed over the sensing area  106  at a predetermined position, in this instance a vertical and horizontal line  806 A-B across the center of the sensing area  106 . When an overlay  802  is placed over the sensing area  106  and the conductive lines  804 A-B on the overlap  802  are not placed over the expected position, as shown in  FIG. 8 , the fingerprint sensor  102  detects a misalignment. The fingerprint sensor  102  may detect a margin of misalignment based on a distance between the conductive ink  804 A-B on the overlay  802  and the expected placement  806 A-B. In such embodiments, if the fingerprint sensor  102  detects a margin of misalignment that exceeds a predetermined threshold, the user may be alerted to replace the overlay  802  in a more accurate manner, for example with a flashing LED indicator. If the margin of misalignment does not exceed the predetermined threshold, the fingerprint sensor  102  may factor the margin of misalignment into the processing of inputs received from a finger through the overlay  802 . Specifically, the fingerprint sensor  102  may adjust the expectation of the position of exposed touch areas based on the detected margin of misalignment. 
     The cross hairs may be replaced by a single detectable dot or a small cross at the centroid of the overlay. In some embodiments, unique detectable patterns may be formed on the overlay configured to impart information to the sensor. For example, the conductive lines  804 A-B forming the cross hairs may each be formed of a unique pattern of dots, dashes, and spaces. The unique pattern may be detected, similar to the pattern of a bar code, and correlated with a specific instruction or other information. For example, the pattern may authenticate the overlay to confirm that the correct overlay is placed on the device. In some embodiments, different overlays may be used for different data input functions. In such embodiments, a unique detectable code may correspond to a particular functionality to thereby cause the fingerprint sensor to be configured in the correct data input mode. 
     The conductive ink  804 A-B on the overlay  802  may allow the fingerprint sensor  102  to detect whether the overlay  802  has been removed. In such embodiments, the fingerprint sensor  102  may be configured not to enter an enrollment mode until the overlay  802  has been removed. In some embodiments, a variety of different overlays—each corresponding to a different data input functionality—may be temporarily placed over the sensing area  106  to operate the fingerprint sensor  102 . Each overlay may have a dedicated conductive ink pattern that the fingerprint sensor  102  can recognize. In some embodiments, certain overlays are restricted from use in relation to the fingerprint sensor  102 . For example, the fingerprint sensor  102  may recognize a restricted overlay based on the dedicated conductive ink pattern and deny access for that particular overlay. 
       FIGS. 9A-9C  illustrate an embodiment of a battery-powered power source  902  in use with the fingerprint sensor  102  installed on the smart card  104 . In some embodiments, the power source  902  (also referred to as a non-data-transmitting power source) is powered by a suitable battery  905 , such as a small cell LR44. Alternatively, the power source  902  may rely on any suitable power element, such as solar or harvested power. The power source  902  may comprise a socket, such as a USB socket, to allow connection of the power source  902  to a main power source. As shown in  FIG. 9A , the power source  902  may include a connector housing (or receptacle)  904  with a slot  908  configured to receive an end of the smart card  104  and contacts  906  (or terminals or electrodes, e.g., flexible conductive pins) within the housing that are connected to the power element (e.g., battery  905 ) according to some embodiments. In some embodiments, the housing  904  is made of injection molded plastic and comprises a minimal number of parts. The housing  904  may be made of a transparent material such that the user may confirm that the power source  902  is used solely for the purpose of providing power to the smart card  104 . The power source  902  is configured to be removably attached to a smart card by inserting the card into the slot  908 , and the contacts  906  within the housing may contact the power transmission contacts of the contact pads  108  (e.g., typically contacts C1 VCC and C5 GND of contact pads  108  of an EMVCo® compliant card of  FIG. 1 ) to thereby electrically connect the smart card  104  to the power element and provide power to the card  104  when inserted into the housing of the power source  902 . In an exemplary embodiment, eight contacts  906  are shown in  FIGS. 9A-C  corresponding to an exemplary pinout as shown in contact pads  108  of  FIG. 1 , but only two contacts  906  are needed to connect to the card  104  to the power transmission contacts when the card is inserted into the housing of the power source  902 . The remaining contacts may be omitted if no data is to be transmitted to or from the card. Removing the card from the housing disconnects the card from the power source. The card  104  may only receive power from the external power source  902  and does not require any additional external electrical connections or wireless connections in order to operate. 
       FIGS. 9D and 9E  show a perspective view and plan view, respectively, of an alternative card holder/power source  910  (also referred to as a non-data-transmitting power source) according to some embodiments.  FIG. 9E  illustrates exemplary, non-limiting dimensions of the holder  910  in millimeters. The holder  910  comprises a slotted housing  912  (also referred to as a receptacle) configured to receive one end of the card  104  (the outline of which is shown in phantom in  FIG. 9D ), a battery holder  914  attached to the housing  912  and configured to hold a suitable battery, connector pins  920  coupled to the battery held in the battery holder  914  and connecting the battery held in the battery holder  914  to the power transmission contacts of the card  104  held in the housing  912 . A retainer arm  916  extends from the housing  912  and includes parallel arms with a lip  918  spanning the ends of the two arms at a distal and thereof for engaging an edge of the card  104 , thereby holding the card  104  in an inserted position with respect to the housing  912 . 
     The power source may comprise one or more LEDs or other status indicators (e.g., visual, audible, tactile indicators) used to indicate the status to the user during enrollment in a situation where there are no status indicators on the smart card itself, where status indicators on the smart card are not suitable, or to supplement status indicators on the smart card. In such embodiments, a component on the smart card  104 , such as the fingerprint sensor, the secure element module, or other processing circuitry, monitors the state of the enrollment process and modulates a power line in the card  104  in a known manner, depending on the state of the enrollment process. The power source may further comprise a detector circuit configured to detect the power line modulation and activate the one or more LEDs accordingly to indicate the correct state of the enrollment process. 
     The power source designs illustrated in  FIGS. 9A-9E  are ideal for providing power to a smart card, however the same design principles may be applied to create power sources for other devices with limited feedback that contain fingerprint sensors. For example, a power source for a fitness monitor would provide power to the fingerprint sensor on the fitness monitor but would need no data connection with the fitness monitor or the fingerprint sensor. 
     Of course, if the device on which the fingerprint sensor is installed is an electronic device having internal power, it may not be necessary to connect the device to an external power source to operate the fingerprint sensor. For example, the device may comprise an internal power source such as a solar cell panel or a battery. 
     There are multiple ways that enrollment mode could be triggered on the card using the power supplied by a power source, such as power source  902 . For example, enrollment mode could be automatically triggered after sensing power to the card for the first time. In some embodiments, enrollment mode could be triggered after an activation code has been successfully entered using a data input device, such as the overlay sticker as shown in  FIGS. 3A-3B . In some embodiments, enrollment mode could be triggered by activating an input mechanism, such as a switch or array of switches located on the power source. In any case, care must be taken to ensure the smartcard is not unintentionally removed from or otherwise disconnected from the external power source during enrollment mode. Thus, for an adhesively held overlay sticker—such as shown in  FIG. 3B  and a card inserted into the slot of a housing of the power source, the sticker must be carefully removed from the card in such a manner as to not remove the card from the housing. The following embodiments encompass power source arrangements that are intended to reduce the likelihood that the card will be disconnected from the power source when the data input device overlay is removed from the fingerprint sensor. 
       FIGS. 9F-9H  illustrate an alternative card holder/power source  920  according to some embodiments.  FIG. 9F  is a plan view with no card inserted in the card holder/power source (also referred to as a non-data-transmitting power source)  920 , and  FIG. 9G  is a cross-sectional view but showing a card inserted in the card holder/power source. In some embodiments, the holder  920  comprises a substrate  922 , for example a single sided PCB, a film, plastic, or cardboard. Card guide rails  924  may be mounted on the substrate  922  and configured to receive one end of the card  104 . A battery holder  926  may be attached to the substrate  922  and configured to hold a suitable battery  928 . Connector pins  930  attached to the substrate between the card guide rails  924  are conductively coupled to the battery  928  via conductive traces on or within the substrate and connect the battery to power transmission contacts  923  of the card  104  held in the card guide rails  924 . The card guide rails  924  may slot around one or more edges of the card  104  to hold it in position. The card guide rails  924  may be adhered directly to the substrate, or held in place with mounting pins  932  which fit into corresponding holes in the substrate. In some embodiments, status indicators  921 , such as LEDs, may be added to the substrate  922 . In an alternative embodiment illustrated in cross-section in  FIG. 9H , the card guide rails  924  may be replaced with a housing  934  configured to receive one end of the card  104  and hold it in position. The housing  934  may be adhered directly to the substrate, or held in place with mounting pins  932  which fit into corresponding holes in the substrate  922 . 
       FIGS. 10A-10E  illustrate an alternative power source with a connector  1002  in use with the fingerprint sensor  102  installed on the smart card  104  according to some embodiments. As shown in  FIG. 10A , the power source (also referred to as a non-data-transmitting power source)  1002  comprises a top cover  1004 , a bottom cover  1006 , and a flap  1010  connected to the bottom cover  1006  with a hinge or foldable connection  1008 . The top cover  1004  is combined with the bottom cover  1006  to form a pocket in which the smart card  104  can be removably received. The bottom cover  1006  is longer than the top cover  1004  by about the width of the flap  1010 . This allows the flap  1010  to flip shut over the bottom cover  1006  to form an extended top cover over the entire area of the bottom cover  1006 . The flap  1010  comprises pierced holes  1014 A-E positioned on a top corner adjacent to the hinge  1008 . The function of the pierced holes  1014 A-E will be described in more detail in  FIG. 10D . The top and bottom covers  1004 ,  1006  form a housing that receives the card. The power source may include a portable power element (e.g., a battery or solar element, not shown), and contact elements (not shown) internal to the housing provide electrical contact to power transmission contacts of the card when the card is inserted into the housing. 
     As shown in  FIG. 10A , the smart card  104  comprises an LED  1012 , contact pads  108  which may be part of a secure element module conforming to the EMVCo® protocol, and a fingerprint sensor  102  comprising a sensing area  106 . In some embodiments, the fingerprint sensor  102  is positioned on one of the uppermost corners of the smart card  104 . 
     As shown in  FIG. 10A , the flap  1010  of the power source (also referred to as a non-data-transmitting power source)  1002  is open and the smart card  104  is positioned so that the smart card  104  may be inserted into the power source  1002  in direction “B.” As shown in  FIG. 10B , the smart card  104  is inserted into the pocket formed by the top and bottom covers  1004 ,  1006  of the power source  1002 . Accordingly, the power source  1002  is removably connected to a power input, such as power transmission contacts of the contact pads  108 , on the smart card  104  and provides power to operate the fingerprint sensor  102 . 
     As shown in  FIG. 10C , once the smart card  104  is fully inserted, the top cover  1004  of the power source  1002  partially covers the surface of the smart card  104 , leaving the fingerprint sensor  102  uncovered. The flap  1010  is then flipped over to close over the uncovered portion of the smart card  104 . In some embodiments, the pierced holes  1014 A-E are located on the flap  1010  such that when the flap  1010  is closed, the pierced holes  1010 A-E expose portions of the sensing area  106  and the LED  1012  to provide a data input device to enable a user to enter a code via the sensor  102 . In some embodiment, the number, size, and position of the pierced holes  1010 A-D may be configured as described in  FIGS. 4-6 . 
     As shown in  FIG. 10D , the pierced holes  1014 A-D are numbered and indicate spatially distinct control areas of the sensing area  106 . The user may enter data, such as a numerical activation code by placing a finger  1015  over the numbered pierced holes  1014 A-D in a specific sequence. The pierced hole  1014 E over the LED  1012  allows the user to receive status indications while entering the data. 
     In other embodiments, the flap  1010  may comprise embedded mechanical buttons instead of the pierced holes  1014 A-D. In such embodiments, when the flap  1010  is closed, the embedded mechanical buttons make contact with the sensing area  106  when pressed by a user. In some embodiments, pads on the embedded mechanical buttons are conductive so that contact with the sensing area  106  may be detected by the sensor. The embedded mechanical buttons may be a dome, plunger, and blister buttons to provide a tactile aspect of the data entry “keys”. 
     As shown in  FIG. 10E , once the user completes data entry (e.g., enters a correct code), the flap  1010  may be opened and the smart card  104  may be removed. The fingerprint sensor may begin a fingerprint enrollment process once the user makes a correct code or data entry. In some embodiments, the flap  1010  is opened and the entire sensing area  106  is revealed in order to proceed with the fingerprint enrollment process. A detectable feature—such a conductive ink mark or pattern—may be provided on the back side of the flap  1010  to allow the sensor  102  to detect whether the flap  1010  is open or closed and/or allow the sensor to calibrate for the exact position of the holes as described above in relation to  FIG. 8 . The smart card  104  may be removed from the power source  1002  in direction “C” after a sufficient fingerprint template of the user&#39;s fingerprint is acquired and stored. 
     The power source  1002  may be used for purposes other than enrollment as described in  FIGS. 10A-10E . For example, the power source  1002  may be used to lock, or temporarily disable, the smart card  104 . In order to lock the smart card  104 , the smart card  104  may be inserted into the power source  1002  as illustrated in  FIGS. 10A-10B . Once the smart card  104  receives power from the power source  1002 , the user may place a finger on the sensing area  106  for verified use of the smart card  104 . Subsequently, the user may flip the flap  1010  over the uncovered portion of the smart card  104  such that the pierced holes  1010 A-E expose portions of the sensing area  106  and the LED  1012  to provide a data input device to enable the user to enter a code via the sensor  102 , as described in  FIGS. 10C-10D . In such embodiments, the user may retrieve a numerical locking code for the smart card  104 . For example, the user may retrieve the numerical locking code through a phone call, an SMS, or an online banking application. Once the user retrieves the numerical locking code, the user may input the locking code by placing a finger over the numbered pierced holes  1014 A-D in a sequence according to the code. As a result of a valid entry of the locking code, the smart card may be locked or temporarily disabled from use. The smart card  104  may be removed from the power source  1002  after the locking process is concluded. The process described above for locking the smart card  104  may be used to unlock the smart card  104 . In another embodiment, the smart card  104  may be unlocked by placing a finger on the sensing area  106  for verification. 
       FIGS. 11A-11C  illustrate another embodiment of a power source (also referred to as a non-data-transmitting power source)  1102  in use with the fingerprint sensor  102  installed on the smart card  104 . As shown in  FIG. 11A , the smart card  104  may be already removably received in the power source  1102 , which may comprise an envelope-like housing configured to receive an end of the card and provide electrical contact between a power element (e.g., a battery or solar element) and the card. The power source  1102  only partially covers the smart card  104  so that the portion containing the fingerprint sensor  102  is exposed. A continuous sleeve  1104  wraps around a bottom end of combined power source  1102  and around the left, right, and bottom ends of smart card  104  to keep the smart card  104  in place within the power source  1102  housing. A data input device in the form of a sleeve  1106  may be used to cover the portion of the smart card  104  containing the fingerprint sensor  102 . In some embodiments, the sleeve  1106  overlaps one end of the continuous sleeve  1104 . Pierced holes  1108 A-E located on the sleeve  1106  expose portions of the sensing area  106  and an LED  1110  on the fingerprint sensor  102 . In an embodiment, a battery connection tab  1112  may be provided between the power source  1102  and the smart card  104  to keep a power connection disconnected until ready for use. The user may pull out the battery connection tab  1112  in direction “D,” as shown in  FIG. 11A , to connect the power source  1102  to the smart card  104  in order to operate the fingerprint sensor  102 . 
     The pierced holes  1108 A-D may be numbered and indicate spatially distinct control areas on the fingerprint sensor  102  as shown in  FIG. 11A . Accordingly, once the user connects the smart card  104  to the power source  1102 , the user may enter data, such as a numerical activation code by placing a finger over the pierced holes  1108 A-D in a specific sequence. The pierced hole  1108 E over the LED  1110  allows the user to receive status indications while entering the data. Once the user has correctly input the data and the fingerprint sensor is ready to initiate enrollment mode, the sleeve  1106  may be slid off the smart card  104  in direction “E,” as shown in  FIG. 11A , while the continuous sleeve  1104  remains intact to keep the card  104  inserted in the power source  1102 . 
     As shown in  FIG. 11B , sliding off the sleeve  1106  reveals a corner of the smart card  104  containing the fingerprint sensor  102 . A detectable feature—such as a conductive ink mark or pattern—may be provided on an inner surface of the sleeve  1106  to allow the sensor  102  to detect if the sleeve  1106  is in place. Upon initiation of the enrollment mode, the user may place a finger on the sensing area  106 . After a sufficient fingerprint template of the user&#39;s fingerprint is acquired and stored by the fingerprint sensor  102 , the continuous sleeve  1104  may be slid off in direction “F,” as shown in  FIG. 11B . After the continuous sleeve  1104  is slid off, the smart card  104  may be removed from the power source  1002  in direction “E”, as shown in  FIG. 11C . 
       FIGS. 12A-12C  illustrate another embodiment of a power source (also referred to as a non-data-transmitting power source)  1202  in use with the fingerprint sensor  102  installed on the smart card  104 . As shown in  FIG. 12A , the smart card  104  may be already removably received in the power source  1202 , which may comprise an envelope-like housing configured to receive an end of the card and provide electrical contact between a power element (e.g., a battery or solar element) and the card. The power source  1202  only partially covers the smart card  104  such that the portion containing the fingerprint sensor  102  is exposed. A data input device in the form of a sleeve  1204  is used to cover the portion of the smart card  104  containing the fingerprint sensor  102 . One side of the sleeve  1204  comprises pierced holes  1206 A-E which expose portions of the sensing area  106  and an LED  1208  on the fingerprint sensor  102 . A detectable feature—such as a conductive ink mark or pattern—may be provided on an inner surface of the sleeve  1204  to allow the sensor  102  to detect whether the sleeve  1204  is in place. In some embodiments, a battery connection tab  1210  is inserted between the power source  1202  and the smart card  104  to keep a power connection disconnected. The user may pull out the battery connection tab  1210  in direction “D,” as shown in  FIG. 12A , to connect the power source  1102  to the smart card  104  in order to operate the fingerprint sensor  102 . 
     The pierced holes  1206 A-D may be numbered and indicate spatially distinct control areas on the fingerprint sensor  102  as shown in  FIG. 12A . In such embodiments, once the user connects the smart card  104  to the power source  1202  by inserting the card into the power source envelope  1202  or by removing the tab  1210  from the power source  1202  in which the card is already inserted, the user may enter data, such as a numerical activation code by placing a finger over the pierced holes  1206 A-D in a specific sequence. The pierced hole  1206 E over the LED  1110  allows the user to receive status indications while entering the data. Once the user has correctly input the data, the sleeve  1204  may be slid off of the smart card  104  in direction “E,” as shown in  FIG. 12A . 
     In some embodiments, once the sleeve  1204  has been slid off, a user can flip the sleeve  1204  over to reveal the finger guide  1212  and slide the sleeve  1204  back over the smart card  104  in direction “B,” as shown in  FIG. 12B . The finger guide  1212  may be a cutout window that indicates to the user where to place a finger on the sensor during the enrollment mode. The sleeve  1204  may then be removed from the smart card  104  after a sufficient fingerprint template of the user&#39;s fingerprint is acquired and stored by the fingerprint sensor, and the smart card  104  is then removed from the power source  1202  in direction “E,” as shown in  FIG. 12C . 
       FIG. 13  illustrates an application of another embodiment of a data input device in the form of an overlay  1302  placed over the sensing area  106  of the fingerprint sensor installed on the smart card  104 . In the illustrated embodiment shown in  FIG. 13 , a smart card is the device containing the fingerprint sensor, but the application of the data input device is not restricted to a smart card and can be used for any device that contains a fingerprint sensor in alternative embodiments. As shown in  FIG. 13 , the overlay  1302  is removably placed over a portion of the card  104  including the sensing area  106  (as shown by the dotted lines in  FIG. 13 ). The overlay  1302  may comprise data input keys  1304 A-D associated with (e.g., coupled to) spatially distinct sensing areas on the sensing area  106  of the fingerprint sensor. The data input keys  1304 A-D are remotely located from the sensing area  106 . In some embodiments, the overlay  1302  may comprise one or more additional pierced holes to indicate spatially distinct control areas of the sensing area  106 , as shown in  FIG. 13 , in addition to data input keys  1304 A-D remotely located from the sensing area  106 . As shown in  FIG. 13 , portions of the sensing area associated with the data input keys  1304 A-D do not overlap with the spatially distinct control areas of the sensing area indicated by the one or more additional pierced holes. In some embodiments, the overlay  1302  may comprise a pierced hole  1306  over the LED  308  or other indicator element on the card  104  when the overlay  1302  is temporarily placed over a portion of the card  104  including the sensing area  106  and the LED  308 . In some embodiments, an OLED display may operate as the fingerprint sensor. In such embodiments, a portion of the OLED display may be configured to be used as the indicator element. Accordingly, the pierced hole  1306  may be positioned over the portion of the OLED display configured to be used as the indicator element. 
     When the fingerprint sensor is used in data input mode, each data input key  1304 A-D can function to enable the user to enter numbers (e.g., an activation code, such as a PIN code) by tapping his or her finger on the spatially distinct control areas  1304 A-D. Each data input key  1304 A-D of the overlay  1302  is electrically coupled to an associated spatially distinct portion of the sensing area  106  so that contact with each key will result in a detectable signal from the sensor element(s) of the associated spatially distinct portion of the sensing area  106 . The coupling between the keys  1304 A-D and the sensing area  106  allows the keys  1304 A-D to be remotely located from the sensing area  106 . This provides the significant advantage of positioning keys  1304 A-D in locations not restricted by the boundaries of the sensing area  106 . For example, extra space on the smart card  104  may be used to provide additional keys (e.g., more than four keys) or the keys  1304 A-D can be spaced further apart, which may improve access for the user. In some embodiments, the overlay  1302  may comprise one data input key electrically coupled to an associated spatially distinct portion of the sensing area  106  configured to receive a Morse code-type data input by the user. 
     As shown in  FIG. 13 , the data input keys  1304 A-D may be spaced out on the overlay  1302  along a short edge of the smart card  104 . The data input keys  1304 A-D may be spaced out on the overlay  1302  along a long edge of the smart card  104 . In other embodiments, the data input keys  1304 A-D may be distributed on the overlay  1302  in the middle of the smart card  104 , rather than being restricted to the short or long edge. The data input keys  1304 A-D may be arranged in various suitable formats depending on the application. For example, the data input keys  1304 A-D may be arranged in a 2-D matrix format, a keyboard format, or a calculator pad format. 
     Power must be applied to the card  104  throughout a data input and enrollment process. In a non-limiting exemplary embodiment, a battery-powered power source, as shown in  FIG. 9A , may be configured to be removably attached via contact pads  108  to the external battery-powered power source. A small tab  1310  extending from one side or corner of the overlay  1302  maybe provided to facilitate grasping the overlay  1302  so that the user may peel off the overlay  1302  with ease. Care should be taken, however, to ensure that the card is not unintentionally disconnected from the power source in the process of peeling the overlay  1302  off the card  104 . In some embodiments, the small tab  1310  is on an edge or corner of the overlay  1302  which encourages the user to peel off the overlay  1302  in a direction moving towards the power source, rather than pulling away from the power source, to avoid dislodging the card from the power source. 
     The card  104  may include an LED  308  or other indicator element, and the overlay  1302  may comprise a pierced hole  1306  positioned over the LED  308  allowing the user to see the LED when the overlay  1302  is temporarily placed over a portion of the card  104  including the sensing area  106  and the LED  308 . In other embodiments, the card  104  may include more than one LED  308  or other indicator element. The LED  308  may illuminate and flash to communicate various instructions and confirmations to the user. 
     In some embodiments, the overlay  1302  may be provided as a sleeve configured to be slid over the portion of the smart card  104  containing the sensing area  106 , as shown in  FIGS. 11A and 12A . Data input keys may be located anywhere on a surface of the sleeve. Each data input key may be electrically coupled to an associated spatially distinct data input portion of the sensing area  106  so that contact with each key will result in a detectable signal from the sensor element(s) of the associated spatially distinct data input portion of the sensing area  106 . 
     In some embodiments, the overlay  1302  may be provided as an alternative power source (also referred to as a non-data-transmitting power source), as shown in  FIG. 10A . In such embodiments, the data input keys may be located on the flap of the power source. The flap may comprise conductive traces which electrically couple each data input key to an associated spatially distinct input portion of the sensing area  106 . 
       FIGS. 14A-14C  illustrate an embodiment of a data input device in the form of an overlay  1402  including data input keys coupled to spatially distinct sensing areas on the sensing area of the fingerprint sensor, wherein the data input keys are remotely located from the sensing area. As shown in  FIGS. 14A-14C , the overlay  1402  is a double layered overlay comprising an upper layer  1404  and a lower layer  1406 . The bottom of the lower layer  1406  contacts the surface of the sensing area  106  when the overlay  1402  is placed over the sensing area  106 . The upper layer  1404  and the lower layer  1406  may be made of peel-able film. 
     As shown in  FIG. 14B , the upper layer  1404  may comprise pierced holes  1408 A-D defining the data input keys, a pierced hole  1410  for an LED  308  or other indicator element on the smart card  104 , and a tab  1412  for easy removal of the overlay  1402 . The surface of the edge surrounding each pierced hole  1408 A-D defining the data input keys may be slightly raised so that a user may feel the circumference of the holes when placing a finger over it. 
     As shown in  FIG. 14C , the lower layer  1406  may comprise key traces  1414 A-D, connection traces  1416 A-D, sensing area activation traces  1418 A-D, and a pierced hole  1410  for an LED  308  or other indicator element on the smart card  104 . A conductive material, such as conductive ink, metallization, conductive polymer, or any conductive coating may be used to print or apply the key traces  1414 A-D, the connection traces  1416 A-D, and the sensing area activation traces  1418 A-D onto a surface of the lower layer  1406 . The key traces  1414 A-D may be located remotely from the sensing area activation traces  1418 A-D. The connection traces  1416 A-D may connect the key traces  1414 A-D to each respective, associated sensing area activation trace  1418 A-D. The sensing area activation traces  1418 A-D are located on the lower layer  1406  so that the sensing area activation traces  1418 A-D align with the associated spatially distinct data input regions of the sensing area  106  when the overlay  1402  is temporarily placed over the smart card  104 . In some embodiments, the material of the lower layer  1406  is a thin polymer, typically no more than 50-100 microns in thickness. The material and thickness of the lower layer  1406  should be such as to not negatively impact the electrical coupling of the sensing area activation traces  1418 A-D with the associated spatially distinct data input regions of the sensing area  106 . In some embodiments, reference traces may be printed or otherwise applied or embedded between each sensing area activation trace  1418 A-D on the surface of the lower layer  1406  so that the reference traces align with associated spatially distinct reference regions of the sensing area  106 . The alignment of the sensing area activation traces  1418 A-D in relation to the sensing area  106  is described in further detail in  FIGS. 15A-15B  and  FIGS. 19A-19D . 
       FIG. 14A  illustrates a surface of the double sided overlay  1402  when the upper layer  1404  is combined with the lower layer  1406  according to some embodiments. When combined, the data input keys are defined by the key traces  1414 A-D visible and accessible through the pierced holes  1408 A-D. The connection traces  1416 A-D and the sensing area activation traces  1418 A-D are covered by the upper layer  1404  and obscured from view. In addition, the upper layer  1404  may be formed from an electrically insulating material to isolate the connection traces  1416 A-D and the sensing area activation traces  1418 A-D. 
       FIG. 15A  illustrates the data input device in the form of a double layered overlay  1402  (the upper layer  1404  is not shown) temporarily placed over the smart card  104  according to some embodiments. As shown in  FIG. 15A , the double layered overlay  1402  covers a portion of the smart card  104  containing the sensor area  106 . The overlay  1402  is placed on the smart card  104  so that the sensing area activation traces  1418 A-D on the lower layer  1406  are covering and aligned with the spatially discrete regions of the sensing area  106  (encompassing one or more specified sensor elements) associated with each key  1414 A-D. 
     The sensing area  106  may be a sensor grid comprising spatially separated rows and columns of drive lines and pickup lines forming an array of sensor elements at overlapping locations of drive lines and pickup lines. The fingerprint sensor may be pre-programmed with expected positions of the sensing area activation traces  1418 A-D corresponding to specific sensor elements on the sensing area  106 . For example, the fingerprint sensor may be pre-programmed to expect the sensing area activation traces  1418 A-D to cover certain rows (or portions thereof) and columns (or portions thereof) of the sensing area  106  and the associated sensor elements of the rows and columns. For example, when a finger contacts a key trace  1414 A, labeled “1,” the respective sensing area activation trace  1418 A is connected to ground through connection trace  1416 A, thereby changing the signal detected at the pickup lines (or portions thereof) (i.e., the sensor elements) covered by the sensing area activation trace  1418 A. Based on the location of the detected portion of the sensing area  106 , the fingerprint sensor is able to determine which key trace  1414 A-D has been contacted by the finger and conclude the associated data input, which is “1” in this scenario. 
     Each of the sensing area activation traces  1418 A-D may be positioned to cover a portion of the sensing area  106 . As shown in  FIG. 15A , the sensing area  106  comprises a grid of overlapping drive lines and pickup lines as described above and each of the sensing area activation traces  1418 A-D may have an elongated configuration oriented in substantially the same direction as the pickup lines. Each of the sensing area activation traces  1418 A-D may overlap a substantial portion of at least one pickup line. In some embodiments, each of the sensing area activation traces  1418 A-D may overlap all of the at least one pickup line. In some embodiments, each of the sensing area activation traces  1418 A-D may overlap a substantial portion of at least four or more pickup lines. In some embodiments, each of the sensing area activation traces  1418 A-D may overlap all of the at least four or more pickup lines. In some embodiments, the sensing area activation traces  1418 A-D are transverse with the pickup lines of the sensing area  106 . 
     In some instances, the double layered overlay  1402  may be misaligned with the sensing area  106 . Accordingly, the sensing area activation traces  1418 A-D may be placed over the sensing area  106  misaligned with the expected positions pre-programmed into the fingerprint sensor. The double layered overlay  1402  may comprise detectable features and the location of such features as detected by the fingerprint sensor may indicate the position of the overlay  1402  with respect to the sensing area  106 . A method of calibration for the fingerprint sensor based on the detectable features provided on the double layered overlay  1402  is described in more detail in  FIG. 8 . Accordingly, the fingerprint sensor may detect a margin of misalignment between the sensing area activation traces  1418 A-D and the expected positions on the sensing area, and factor the margin of misalignment into the processing of inputs received through each sensing area activation trace  1418 A-D. 
     The detectable features provided on the double layered overlay  1402  with respect to the sensing area  106  may comprise conductive lines forming a unique pattern of dots, dashes, and spaces. The unique pattern may be detected, similar to the pattern of a bar code, and correlated with a specific instruction or other information. For example, the pattern could authenticate the overlay  1402  to confirm that the correct overlay is placed on the card. In a situation in which different overlays may be used for different data input functions, the unique detectable code can correspond to the particular functionality to thereby cause the fingerprint sensor to be configured in the correct data input mode. 
     In some embodiments, the detectable features provided on the double layered overlay  1402  with respect to the sensing area  106  allow the fingerprint sensor to detect whether the overlay  1402  has been removed. In such embodiments, the fingerprint sensor may be configured not to enter an enrollment mode until the overlay  1402  has been removed. In some embodiments, a variety of different overlays—each corresponding to a different data input functionality—may be temporarily placed over the sensing area  106  to operate the fingerprint sensor. Each overlay may have a dedicated conductive ink pattern that the fingerprint sensor can recognize. In some embodiments, certain overlays may be restricted from use in relation to the fingerprint sensor. In such embodiments, the fingerprint sensor may recognize a restricted overlay based on the dedicated conductive ink pattern and deny access for that particular overlay. 
     In some embodiments, the sensing area  106  comprises a linear array of sensor elements, as shown in  FIG. 15B . Exemplary embodiments of linear arrays of sensor elements are described in U.S. Pat. No. 7,110,577, entitled “Method and Apparatus for Measuring Structures in a Fingerprint” and U.S. Pat. No. 7,751,601, entitled “Fingerprint Sensing Assemblies and Methods of Making,” the respective disclosures of which are incorporated by reference in their entirety. As shown in  FIG. 15B , the overlay  1402  is placed on the smart card  104  so that the sensing area activation traces  1418 A-D on the lower layer  1406  are covering spatially discrete portions of the sensing area  106  (encompassing one or more specified sensor elements of the linear array) associated with each key  1414 A-D. 
       FIG. 15C  illustrates a magnified view of the sensing area activation traces  1418 A-D placed over the sensing area  106  according to some embodiments. As shown in  FIGS. 15A and 15C , reference traces  1502 A-C may be printed or otherwise applied onto or embedded into a surface of the lower layer  1406  between each of the sensing area activation traces  1418 A-D such that the reference traces  1502 A-C align with associated spatially distinct reference regions of the sensing area  106 . The sensing area activation traces  1418 A-D are connected through connection traces  1416 A-D to the key traces  1414 A-D. The reference traces  1502 A-C are not connected to the key traces  1414 A-D and may be utilized to employ a differential signal detection structure for the fingerprint sensor  102 . As shown in  FIG. 15D , sensor elements covered by a sensing area activation trace  1418 A are connected to a positive input  1503 A of a differential amplifier  1504  located in the fingerprint sensor, and sensor elements covered by an adjacent reference trace  1502 A are connected to a negative input  1503 B of the differential amplifier  1504  according to some embodiments. The reference trace  1502 A may be subject to noise and unwanted signal inputs similar to that of the sensing area activation trace  1418 A. In some embodiments, when a finger contacts a key trace  1414 A, the contact by the finger completes the circuit connecting key trace  1414 A to ground  1506 , thereby changing pickup signals detected in the sensor elements covered by the activation trace  1418 A. In such embodiments, the differential amplifier  1504  may be configured to subtract the pickup signals of the sensor elements covered by reference trace  1502 A from the pickup signals of the sensor elements covered by activation trace  1418 A, thereby eliminating the noise and unwanted signal inputs affecting both pickup signals equally, and leaving substantially only the signal variation in the sensor elements covered by the activation trace  1418 A due to contact with the key trace  1414 A. Thus, the sensor eliminates noise by subtracting the pickup signals of the sensor elements covered by a reference trace  1502 A signal from the pickup signals of the sensor elements covered by an activation trace  1418 A-D at the differential amplifier  1504 . The use of reference traces  1502 A-C to eliminate noise allows a better detection rate for the keys. In some embodiments, one reference trace  1502 A may be used to eliminate noise for all of the sensing area activation traces  1418 A-D. 
       FIGS. 15E-15H  illustrate embodiments of conductive material arrangement on the data input device in the form of an overlay when temporarily placed over the sensing area of the fingerprint sensor. As shown in  FIG. 15A , the conductive material comprises four sensing area activation traces  1418 A-D connected to four key traces  1414 A-D (not shown in  FIG. 15E ) via connection traces  1416 A-D and three reference traces  1502 A-C. In some embodiments, the four activation traces  1418 A-D facilitate a 4 key data input device. As shown in  FIG. 15E , each reference trace  1502 A-C is positioned between a two sensing area activation trace  1418 A-D. The traces placed over the sensing area  106  are separated by a predetermined gap  1504 . The width of the sensing area activation traces  1418 A-D, the reference traces  1502 A-C, and the gap  1504  may be determined based on the choice of conductive material used to print or insert the traces on the overlay and on the sensing area  106 . For example, an achievable printer resolution may govern the minimum value of the width of the traces and the gap  1504  if conductive ink is used as the conductive material. 
     A single reference trace  1502 A-C may be used for two or more sensing area activation traces  1418 A-D provided that the sensor elements associated with the two or more sensing area activation traces  1418 A-D are not to be sensed simultaneously when sharing the single reference trace  1502 A-C. For example, a first sensing area activation trace  1418 A may use a reference trace  1502 A and a second sensing area activation trace  1418 B may also use the reference trace  1502 A for differential signal detection. In such embodiments, sensor elements associated with the first sensing area activation trace  1418 A and the second sensing area activation trace  1418 B should not be sensed simultaneously when sharing the single reference trace  1502 A. In some embodiment, the second sensing area activation trace  1418 B can use a second reference trace  1502 B. 
       FIG. 15F  illustrates another embodiment of arranging conductive material over the sensing area of the fingerprint sensor. As shown in  FIG. 15F , reference traces are not used and only sensing area activation traces  1418 A-D are placed over the sensing area  106  of the fingerprint sensor  102 . Each of the sensing area activation traces  1418 A-D are separated by a predetermined gap  1504 . In some embodiments, the sensing area activation traces  1418 A-D are evenly distributed over the sensing area  106 . In other embodiments, the sensing area activation traces  1418 A-B are not evenly distributed over the sensing area  106  and concentrated on a specific portion of the sensing area  106 , as shown in  FIG. 15G . The sensing area activation traces  1418 A-B may be in any shape or size, as shown in  FIG. 15H . As shown in  FIG. 15H , the sensing area activation traces  1418 A-B are not restricted to the shape of a strip having a length corresponding to the width of the sensing area along direction “G.” For example, the sensing area activation traces  1418 A-B may be in the shape of square or rectangle blocks on the sensing area. When the sensing area activation traces  1418 A-B are in the shape of a square or a rectangle block, there may be a loss in detection sensitivity because the sensing area activation traces  1418 A-B are not aligned with the full length of the pickup lines of the sensing area  106 . In order to compensate for any loss in detection sensitivity, the square or rectangle block sensing area activation traces  1418 A-B are wider along the sensing area length, i.e., direction “H,” in order to cover more pickup lines. In some embodiments, the area of a square or rectangle block sensing area activation trace  1418 A-B is the equivalent of an area of a sensing area activation trace in the shape of a strip as illustrated in  FIG. 15G . Accordingly, a square or rectangle block sensing area activation trace  1418 A-B may cover the same area of the sensing area  106  as a sensing area activation trace  1418 A-B in the shape of a strip and therefore cover the same number of pickup/drive line overlaps (i.e., sensor elements) as the strip-shaped activation trace. 
       FIG. 16A  illustrates an embodiment of an alternative noise reduction concept in which the data input device comprises one or more keys  1614  formed as interdigitated plates  1608 A-B. In some embodiments, each of the one or more keys  1614  comprises a first plate  1608 A and a second plate  1608 B. As shown in  FIG. 16A , the first plate  1608 A is connected to a first sensing area activation trace  1610 A and the second plate  1608 B is connected to a second sensing area activation trace  1610 B. Accordingly, each key  1614  may be associated with sensor elements covered by two sensor activation traces  1610 A,  1610 B. Sensor elements covered by the first sensing area activation trace  1610 A may be connected to a negative input  1611 B of the differential amplifier  1604  and sensor elements covered by the second sensing area activation trace  1610 B may be connected to a positive input  1611 A of the differential amplifier  1604 . In some embodiments, drivers  1609 A-B may drive the positive input  1611 A 180 degrees out of phase with the negative input  1611 B of the differential amplifier  1604 . In some embodiments, when a finger contacts the key  1614  and simultaneously contacts first and second plates  1608 A and  1608 B, the contact by the finger completes the circuit by connecting key  1614  to ground  1606 A-B, thereby changing pickup signals detected in the sensor elements associated with the activation traces  1610 A-B. In such embodiments, the differential amplifier  1604  subtracts the pickup signals of sensor elements associated with the first sensing area activation trace  1610 A from the pickup signals of the sensor elements associated with the second activation trace  1610 B, thereby eliminating the noise and unwanted signal inputs affecting both pickup signals equally and acquiring a differential signal that would be easily detected by the fingerprint sensor. 
       FIG. 16B  illustrates an embodiment of an alternative noise reduction concept in which the data input device comprises one or more keys  1624  formed as split plates  1618 A-B. In some embodiments, each of the one or more keys  1624  comprises a first plate  1618 A and a second plate  1618 B. As shown in  FIG. 16B , the first plate  1618 A is connected to a first sensing area activation trace  1620 A and the second plate  1618 B is connected to a second sensing area activation trace  1620 B. Accordingly, each key  1624  is associated with sensor elements covered by two sensor activation traces  1620 A,  1620 B. Sensor elements covered by the first sensing area activation trace  1620 A are connected to a negative input  1621 B of a differential amplifier  1616  and sensor elements covered by the second sensing area activation trace  1620 B are connected to a positive input  1621 A of the differential amplifier  1616 . In some embodiments, drivers  1619 A-B drive the positive input  1621 A 180 degrees out of phase with the negative input  1621 B of the differential amplifier  1604 . In some embodiments, when a finger contacts the key  1624  and simultaneously contacts first and second plates  1618 A and  1618 B, the contact by the finger completes the circuit by connecting key  1624  to ground  1606 A-B, thereby changing pickup signals detected in the sensor elements covered by the activation traces  1620 A-B. In such embodiments, the differential amplifier  1616  subtracts the pickup signals of sensor elements covered by the first sensing area activation trace  1620 A from the pickup signals of the sensor elements covered by the second sensing area activation trace  1620 B, thereby eliminating the noise and unwanted signal inputs affecting both pickup signals equally and acquiring a differential signal that would be easily detected by the fingerprint sensor. 
       FIG. 17  is a cross sectional view of an embodiment of the data input device in the form of an overlay  1702  which creates data input keys coupled to associated spatially distinct data input sensing areas on the sensing area of the fingerprint sensor. In some embodiments, the data input key is located on a first side of the overlay  1702  and the overlay  1702  includes a conductive trace extending through the overlay  1702  to a conductive trace connected to an associated spatially distinct data input area on an opposite side of the overlay. As shown in  FIG. 17 , the overlay  1702  is a single layer overlay and conductive material may be printed or otherwise applied on or embedded in a top and a bottom surface of the single layer overlay  1702  and through the single layer overlay  1702  to connect the conductive material on both surfaces. In some embodiments, the conductive material printed or applied on the top surface of the single layer overlay  1702  forms one or more key traces  1706 . The conductive material printed or applied on the bottom surface of the single layer overlay  1702  covering and aligned with a portion of the sensing area  106  forms one or more sensing area activation traces  1704 . The one or more key traces  1706  and the one or more sensing area activation traces  1704  are connected by one or more connection traces  1708  extending along the bottom surface and through the overlay  1702 . In some embodiments, each of the one or more key traces  1706  is connected to an associated spatially distinct sensing area activation trace  1704  by a dedicated connection trace  1708 . Each of the one or more connection traces  1708  are spatially distinct. The single layer overlay  1702  may be formed from an electrically insulating material to isolate each of the one or more key traces  1706 , connection traces  1708 , and sensing area activation traces  1704 . The function and description of the key traces  1706 , connection traces  1708 , and sensing area activation traces  1704  are described in more detail in  FIGS. 14A-14C  and  FIGS. 15A-15H  above. 
     In some embodiments, the single layer overlay  1702  is made of peel-able film and may be temporarily placed over the smart card  104  by applying a repositionable adhesive. In some embodiments, a small tab may be provided at a side or corner of the single layer overlay  1702  so that the user may peel off the overlay  1702  with ease. 
       FIG. 18  is a cross sectional view of an embodiment of a data input device in the form of an overlay  1802  secured to opposite sides of a host device and including data input keys on multiple surfaces of the host device that are coupled to associated spatially distinct regions or portions of the sensing area of the fingerprint sensor. As shown in  FIG. 18 , the overlay  1802  is applied to multiple surfaces of the smart card  104  or other type of host device. The overlay  1802  covers the sensing area  106  and provides one or more keys  1806 A-B on the same side of the card  104  as the sensing area  106  and is also wrapped around or folded around the smart card  104  in order to provide the user with one or more data input keys  1806 C on the opposite side of the smart card  104 . In some embodiments, conductive material printed or applied on an outside surface of the overlay  1802  forms the one or more keys  1806 A-C. The conductive material printed or applied on an inside surface, the surface in contact with the smart card  104 , of the overlay  1802 , covering and aligned with a portion of the sensing area  106  forms one or more sensing area activation traces  1808 . The one or more keys  1806 A-C and the one or more sensing area activation traces  1808  are connected by one or more connection traces  1810  extending along the inside surface and through the overlay  1802 . In some embodiments, each of the one or more keys  1806 A-C are connected to an associated spatially distinct sensing area activation trace  1808  by a dedicated connection trace  1810 . Each of the one or more connection traces  1810  are spatially distinct. In some embodiments, the overlay  1802  is formed from an electrically insulating material to isolate each of the one or more keys  1806 A-C, connection traces  1810 , and sensing area activation traces  1808 . The function and description of the key traces  1806 A-C, connection traces  1810 , and sensing area activation traces  1808  are described in more detail in  FIGS. 14A-14C  and  FIGS. 15A-15H  above. 
     The embodiment of the overlay disclosed in relation to  FIG. 18 , where one or more keys  1806 A-B are provided on one side of the card  104  and one or more data input keys  1806 C are provided on the opposite side of the smart card  104 , may improve the convenience of data entry for the user for certain applications. The availability of data input keys  1806 A-C on multiple surfaces increases the variety of data input combinations. The wrap around portion  1804  of the overlay  1802  may be any shape depending on the shape of the smart card  104  or device the overlay  1802  is being wrapped or folded around. The overlay  1802  may be a single layer overlay as described in  FIG. 17 . In other embodiments, the overlay  1802  may be a double layered overlay as described in  FIGS. 14A-C . 
       FIG. 19  illustrates an embodiment of a data input device including data input keys on a remote keypad device and a data transfer cable coupling the data input keys to associated spatially distinct sensing regions on the sensing area of the fingerprint sensor. As shown in  FIG. 19 , an overlay  1908  is electrically attached to an end of a data transfer cable  1906  and temporarily placed over the sensing area  106 . In some embodiments, conductive material may be printed or applied on a bottom surface of the overlay  1908  which contacts the surface of the sensing area  106  when the overlay  1908  is temporarily placed over the sensing area  106 . The conductive material printed or applied on the bottom surface of the overlay  1908  forms one or more sensing area activation traces  1910 , which covers and aligns with a portion of the sensing area  106 . The data transfer cable  1906  couples the one or more sensing area activation traces  1910  to associated data input keys  1904 A-D on a remote keypad device  1902 . The data transfer cable  1906  may be a flexible cable comprising conductive traces to connect the one or more sensing area activation traces  1910  to associated data input keys  1904 A-D on the remote keypad device  1902 . In some embodiments, the remote keypad device  1902  comprises status indicators such as LEDs, a display screen or a sound emitting unit, such as an audio speaker or a vibrator, to provide feedback to the user during data input. 
       FIG. 20  illustrates an embodiment of a data input device including data input keys coupled to associated spatially distinct sensing areas on the sensing area of the fingerprint sensor. In some embodiments, the data input keys  2002 A-J are remotely located from the sensing area  106  and the data input device  2004  extends beyond one or more edges of the host device. As shown in  FIG. 20 , the data input device  2004  covers a portion of the smart card  104 , or any other host device, which contains the sensing area  106  and comprises the data input keys  2002 A-J remotely located from the sensing area  106 . The data input device  2004  may extend off of the smart card  104  in any direction. The data input device  2004  may be in a different shape including a rectangle, a circle, an oval or a lozenge. In some embodiments, repositionable adhesive may be applied to a portion of a bottom surface of the data input device  2004  that overlaps with the surface of the smart card  104 . In some embodiments, lines or other indicia may be provided on the bottom surface of the data input device  2004  to assist the user in properly positioning the data input device  2004  and smart card  104  with respect to each other. 
     In some embodiments, the data input device  2004  comprises one or more data input keys  2002 A-J, each associated with a spatially discrete region of the sensing area  106 . The data input keys  2002 A-J may be located anywhere on the surface of the data input device  2004 . For example, the data input keys  2002 A-J may be positioned on the area of the data input device  2004  that overlies the smart card  104  and/or on the area of the data input device that is not overlying the smart card  104 . Each of the one or more keys  2002 A-J is connected to an associated sensing area activation trace covering a portion of the sensing area  106 . As described above, each key  2002 A-J may comprise a conductive material printed or otherwise applied to the data input device  2004  to form a key trace, a sensing area activation trace covering the associated spatially distinct data input region of the sensing area  106 , and a connection trace connecting the key trace to the sensing area activation trace. The data input device  2004  may be a double layer construction with the conductive portions printed on top of a lower layer made of a thin material that will not negatively impact the electrical coupling of the sensing area activation traces with the associated spatially distinct data input regions of the sensing area  106  and an upper layer made from an insulating material and including holes formed over the key traces. In other embodiments, the data input device may be a single layer construction with traces formed on top of a layer of insulating material, sensing area activation traces formed on the bottom of the layer and connecting traces formed on the top and/or bottom and extending though the layer. 
       FIGS. 21A-21D  illustrates another embodiment of a data input device in the form of an overlay  2102 . In some embodiments, the overlay  2102  comprises a power source (also referred to as a non-data-transmitting power source) for the fingerprint sensor  102  installed on the card  104 . The card  104  comprises the fingerprint sensor  102  with a sensing area  106 , the LED  308 , and the contact pads  108  providing contacts for an external power source. 
     As illustrated in  FIGS. 21A-21B , the overlay  2102  comprises a plurality of data input keys  2106 A-D and a pierced hole  2510  to be placed over an LED  308  of the card  104 . Each of the plurality of data input keys  2106 A-D is directly or indirectly coupled to one or more spatially distinct regions of the sensing area  106 . In some embodiments, the power source of the overlay  2102  is a solar cell panel  2108 . The overlay  2102  may comprise two separate or separable parts  2102   a ,  2102   b . The overlay  2102  may include a perforated line  2112  for separating a portion  2102   a  comprising the solar cell panel  2108  and a portion  2102   b  comprising the plurality of data input keys  2106 A-D. The perforated line  2112  allows a user to easily peel off the portion  2102   b  containing the plurality of data input keys  2106 A-D while the portion  2102   a  containing the solar cell panel  2108  remains attached to the card  104 . The overlay  2102  may comprise, for example, an adhesively-backed label or a sleeve placed over the card in one or two parts. 
     In some embodiments, one or more of the contact pads  108  provide electric contacts between the card  104  and the solar cell panel  2108  contained in the overlay  2102 . 
     The overlay  2102  may be removably placed over a portion of the card  104  including the sensing area  106  and the contact pads  108 , as shown in  FIG. 21C . In some embodiments, the overlay  2102  is operatively placed on the card  104  such that the solar cell panel  2108  is electrically coupled to the contact pads  108  and the data input keys  2106 A-D are electrically coupled to associated spatially distinct data input sensing areas on the sensing area  106 . 
     As shown in  FIG. 21D , a cover overlay  2104  may be removably placed over the solar cell panel  2108  on portion  2102   a  of the overlay  2102 . When the cover overlay  2104  is removably placed over the solar cell panel  2108 , the solar cell panel  2108  cannot generate the power necessary for operation of the fingerprint sensor  102 . Accordingly, the cover overlay  2104  needs to be removed from the overlay  2102  to operate the fingerprint sensor  102 . When exposed, the solar cell panel  2108  provides power through the contact pads  108  for the operation of the fingerprint sensor  102 . The fingerprint sensor  102  may then be activated and enter a data input mode, in which the fingerprint sensor  102  awaits the input of an activation code via the data input keys  2106 A-D. In some embodiments, an indication may be provided to the user via LED  308  to signal to the user that the card is powered and ready to receive an activation code. In some embodiments, instructions may be provided on the cover overlay  2102  to give guidance to the user. For example, the user may be instructed to: (i) call a phone number listed on the cover overlay  2104 , such as, a 1-800 phone number, to retrieve a numerical activation code and (ii) peel off the cover overlay  2104  in order to enter the retrieved numerical activation code. 
     Once the user inputs the correct numerical activation code, the fingerprint sensor  102  enters enrollment mode—e.g., as may be signaled by the LED  308  as described herein. The user may peel off or otherwise remove the portion  2102   b  of the overlay  2102  comprising the data input keys  2106 A-D to expose the sensing area  106  and enroll a fingerprint. Care must be taken to ensure the portion  2102   a  of the overlay is not unintentionally removed from or otherwise dislodged from the card  104  during the enrollment mode or while the portion  2102   b  is being removed. The overlay  2102  may comprise a small tab  2114  sticking out of one side adjacent to the perforated line  2112 , as shown in  FIG. 21C , to help the user easily peel off the portion  2102   a  comprising the data input keys  2106 A-D. After the user successfully enrolls a fingerprint template—e.g., as may be signaled by the LED as described herein—the user may peel off any remaining portions of the overlay  2102 , including the solar cell  2108 , to obtain the functional smart card as shown in  FIG. 21B . 
     In some embodiments, the portion of the overlay  2102  comprising the solar cell panel  2108  may be provided as a power source housing, as described in  FIGS. 11A and 12A . In such embodiments, the overlay does not require a battery connection tab  1112 . Instead, a cover overlay may be removably placed over the solar cell panel. 
     The overlay  2102  may be provided as an alternative power source, as shown in  FIG. 10A . In such embodiments, the solar cell panel and the cover overlay placed over the solar cell panel may be provided on the top cover of the power source and the data input keys may be located on the flap of the power source. 
       FIG. 22  is a flowchart illustrating an embodiment of a simple, cost-effective method  2200  to enroll a biometric template, such as a fingerprint template, on a device that has limited ability to provide feedback to the user, such as a smart card, is described in detail below. In the illustrated embodiment shown in  FIG. 22 , a smart card is assumed to be the device containing the fingerprint sensor, but the method is not restricted to a smart card and can be used for any device that contains a fingerprint sensor in alternative embodiments. A smart card, as defined by the “Smart Card Alliance,” is a device in which an integrated circuit, or chip, is embedded. Smart card technology conforms to international standards ISO/IEC 7816 and ISO/IEC 14443. Accordingly, a person of ordinary skill in the art will understand that a smart card is not restricted to a plastic card. While the plastic card was the initial smart card form factor, technology used for the smart card is now available in a wide variety of form factors, including plastic cards, key fobs, and subscriber identification modules (SIMs) used in GSM mobile phones, watches, electronic passports and USB-based tokens. Smart card applications include, and are not restricted to, bank cards, mobile phone subscriber identification modules (SIM), healthcare cards, government and enterprise ID cards, benefits and social welfare cards, driver&#39;s licenses, physical and logical access cards, mass transit (ticketing) cards, and card that combine multiple applications on a single card, 
     In step  2202 , a data input device, such as the data input device in the form of an overlay as shown in  FIGS. 3B and 13  or the data input device in the form of a sleeve as shown in  FIGS. 10-12 , is temporarily connected to a fingerprint-enabled smart card. In some embodiments, a unique code, such as an activation code, is written into a secure memory of the smart card and encrypted in a secure location during the manufacturing process of the smart card. The fingerprint sensor on the smart card is calibrated during the manufacturing process and set to data-input mode before the smart card is sent to the user. A data input device, such as, for example any of the overlays or sleeves described herein, may be placed on the card as a final or near-final step of the card manufacturing process. The data input device may be temporarily placed over the portion of the card including the sensing area  106  by applying a repositionable adhesive provided by companies such as 3M, Krylon, Franklin Adhesives and Polymers and Bostik. 
     In step  2204 , the card provider provides the smart card and a low-cost, simple power source to the user, e.g., sent by mail or courier or given out by a bank or retail outlet. The power source could be battery powered, powered by mains (e.g., via a USB connector), or solar powered. A non-limiting exemplary embodiment of the power source is described in  FIGS. 9A-9H . In some embodiments, if the smart card contains an on-board power source, the power source need not be provided to the user. 
     The smart card and the power source may be sent to the user with the smart card already inserted in the power source as described in  FIGS. 11A-11C and 12A -C. In such embodiments, a battery connection tab may be inserted between the power source and the smart card to keep a power connection disconnected. The user may pull out the battery connection tab, as shown in  FIG. 12A , to connect the power source to the smart card. 
     In step  2206 , the user follows instructions, received with the card to obtain an activation code from the card provider. For example, the user may be asked to call a number, or the data input device might have a QR® code that the user can scan with a smart phone, or the user could log-in to their on-line banking site or mobile application and indicate they wish to receive an activation code by SMS. In some embodiments, other secure mechanisms for obtaining the activation code are available. In some embodiments, a six-digit activation code provides the user with an appropriate security level. The security level may be increased or decreased by varying the number of required digits, depending on the card provider&#39;s requirements. 
     In step  2208 , if not already done, the user connects the smart card to the power source, for example by inserting the card into a power source housing. The card receives power from the power source, and a status indicator on the smart card (e.g., an LED) indicates to the user that the smart card is ready. 
     In step  2210 , the user enters the activation code by sequentially touching the data input keys of the data input device in a sequence corresponding to the activation code, for example, as described in  FIGS. 2A, 3A-3B, 10D, 11A, 12A, 13, 17, 18, 19 and 20 . The fingerprint sensor may be configured to simply detect presence of the finger on the remote or direct-contact data input key in the code entry and unlock mode. In some embodiments, the fingerprint sensor may be configured to detect fingerprint ridges and valleys in the code entry and unlock mode. 
     In some embodiments, the fingerprint sensor may comprise a status indicator configured to indicate to the user that the entered code is correct or incorrect. If the entered code is incorrect, the user may make a pre-determined number of additional attempts before the smart card locks the user out permanently. For example, the user may get three attempts to correctly enter the code. In some embodiments, if the number of unsuccessful attempts reaches the limit or the activation code is not entered before a pre-set time has passed, the smart card locks the user out permanently. 
     In some embodiments, if one or two unsuccessful entries have been made, the number of unsuccessful entries is stored in a non-volatile memory. In such embodiments, even if power to the smart card is disconnected and reapplied, the smart card still remembers how many unsuccessful entries have been made. Accordingly, the card cannot be “re-set” to a full complement of attempts by disconnecting the card after a number of unsuccessful attempts that is less than the maximum allowed number of attempts. 
     A smart card “state” may be stored in the non-volatile memory of the card. For example, different states may include: (i) “new state” meaning the card is awaiting unlock by entry of a valid activation code; (ii) “unlocked state” meaning that the card is unlocked but enrollment has not been successfully completed; (iii) “active state” meaning that the card is unlocked and an enrollment has been successfully completed; and (iv) “locked state” meaning that the card unlock procedure has been unsuccessfully attempted. 
     In step  2212 , if the activation code has been entered correctly, the user can now remove the data input device from the card and start to enroll a fingerprint (enrollment mode). The smart card must remain connected to the power source throughout the enrollment process. The status indicator makes an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for a fingerprint template, e.g., by the LED illuminating for longer period, such as 10 or more seconds. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     In some embodiments, the user may trigger the enrollment mode by correctly entering the activation code and not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any or sufficient input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     In step  2214 , the user removes the smart card from the power source, and the power source may be discarded. 
     Accordingly, the user has now successfully enrolled a fingerprint in the smart card through the simple, cost-effective method  2200  and can use the smart card in the normal way to pay for items, but now requiring fingerprint verification in order to use the smart card. In some embodiments, multiple users may enroll a fingerprint on the smart card, or a user may enroll multiple fingers on the smart card, using the above noted method  2200 . In such embodiments, the card may be programmed with multiple activation codes that are provided to each user. For each method  2200 , a new activation code is required and entered to enroll a new user/finger. 
     In some embodiments of the method  2200 , the data input device may be provided as a sleeve and guide the user for activation code entry as described in  FIGS. 11A-11C and 12A-12C . 
     In some embodiments of the method  2200 , the overlay may be not required to guide the user for activation code entry. In such embodiments, the power source may comprise a pierced flap to guide the user, as described in  FIGS. 10A-10E , and the overlay need not be placed on the card as part of a manufacturing process of the card. 
     In some embodiments of the method  2200 , the power source may comprise a display screen, speakers, and may include a socket for headphones. In such embodiments, the smart card may provide status indications throughout the enrollment process through the display screen and speakers contained in the power source. 
       FIG. 23A  is a flowchart illustrating another embodiment of a simple, cost effective method  2300  to enroll a biometric template, such as a fingerprint template, on a device that has limited ability to provide feedback to the user, such as a smart card, without requiring entry of activation data (i.e., an activation code) prior to enrolling the fingerprint template. 
     In step  2302 , a fingerprint-enabled smart card is manufactured. During the manufacturing process, the fingerprint sensor on the fingerprint-enabled smart card is configured to be in a default “enrollment mode” when connected to a power source. The card provider may optionally set the status of the smart card as inactive to prevent unauthorized use before the intended user can enroll a fingerprint template and contact the card provider to activate the card. 
     In step  2304 , the card provider provides the smart card and a low-cost, simple power source to the user, e.g., sent by mail or courier or given out by a bank or retail outlet. The power source may be battery powered, powered by mains (e.g., via a USB connector), or solar powered. A non-limiting exemplary embodiment of the power source is described in  FIGS. 9A-9H . In some embodiments, if the smart card contains an on-board power source, such as a solar cell, an external power source is not required. 
     In step  2306 , the user connects the smart card to the power source by, for example, inserting the card into a power source housing having contacts for connecting one or more power transmission contacts of the smart card to the power source without connecting any data transmission contacts of the smart card to a device configured to transmit data to or receive data from the card. Accordingly, connecting the smart card to the power source does nothing but provide power to the electrical components of the smart card—e.g., LED, logic elements, sensor elements, etc.—and the power source is unable to transmit data to or from the smart card. 
     The smart card and the power source may be sent to the user with the smart card already inserted in the power source as described in  FIG. 9A . In such embodiments, a battery connection tab is inserted between the power source and the smart card to keep a power connection disconnected. The user may pull out the battery connection tab, as shown in  FIG. 12A , to connect the power source to the smart card. 
     Connection to the power source may automatically activate the enrollment mode in the fingerprint sensor. In some embodiments, the enrollment mode in the fingerprint sensor is activated once upon a specific instance of connecting the card to the power source (e.g., the first, second, third, etc. connection of the smart card to the power source). The card remains in enrollment mode until disconnected from the power source or until the enrollment is complete. If the card is disconnected from the power source before enrollment is complete, the card cannot again be put into enrollment mode by re-connecting the card to the power source, and the user may be required to take some action, such as contact the card provider or obtain a new card, to enable the card to be put into enrollment mode. 
     The user may trigger the enrollment mode by connecting the card to the power source and not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any or sufficient input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     In other embodiments, the enrollment mode in the fingerprint sensor is activated each time the smart card is connected to the power source until a fingerprint template is stored. In yet another embodiment, enrollment mode in the fingerprint sensor may be activated each time the smart card is connected to the power source until a fingerprint template has been stored after the initial automatic activation upon the specific instance of connecting the smart card to the power source. 
     The card receives power from the power source, and a status indicator on the smart card (e.g., an LED) indicates to the user that the one or more power transmission contacts of the power source are connected to the power source (i.e., the card is powered), that the fingerprint sensor is in enrollment mode, and the smart card is ready for enrollment to start. 
     In step  2308 , the user can now start to enroll a fingerprint. The fingerprint is enrolled by storing a fingerprint template derived from one or more fingerprint images generated by placing a finger on the fingerprint sensor. The smart card must remain connected to the power source throughout the enrollment process. In the event the smart card is disconnected from the power source during the enrollment process, the enrollment mode in the fingerprint sensor is automatically deactivated. In some embodiments, reconnecting the smart card to the power source automatically activates the enrollment mode in the fingerprint sensor until a fingerprint template is stored. That is, enrollment mode may be automatically activated upon application of power to the card if the card logic detects that no fingerprint template has been stored for the card. The enrollment process is complete when a sufficient fingerprint template is acquired and stored in the fingerprint sensor (e.g., as described in previously incorporated U.S. Pat. No. 9,684,813). Once the enrollment process is complete, enrollment mode in the fingerprint sensor is disabled. Accordingly, connecting the smart card to the power source after a successful enrollment will no longer activate the enrollment mode in the fingerprint sensor. In some embodiments, the status indicator provides an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for the fingerprint template and confirm that the enrolling step is successfully complete, e.g., by the LED illuminating for longer period, such as 10 or more seconds. In other embodiments, more than one LED may flash different colors to communicate the various indications described above. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     In step  2310 , the user removes the smart card from the power source, thereby disconnecting the one or more power transmission contacts of the smart card from the power source, and the power source may be discarded. 
     If the card provider set the status of the card as inactive at step  2302 , then the user must activate the card before attempting to use it. In step  2312 , the user contacts the card provider (e.g., by phone, app, internet, etc.) to activate the smart card. The user must provide acceptable user verification details to the card provider in order to activate the smart card. If the user is verified, the card provider sets the card status as active in their systems. The user is now able to use the card in the normal way to pay for items, but now requiring fingerprint verification in order to use the smart card. If the user is not verified, the card remains inactive and cannot be used. 
       FIG. 23B  is a flowchart illustrating another embodiment of a simple, cost effective method  2314  to enroll a biometric template, such as a fingerprint template, on a device that has limited ability to provide feedback to the user, such as a smart card, without requiring entry of activation data (i.e., an activation code) prior to enrolling the fingerprint template. 
     In step  2316 , a fingerprint-enabled smart card is manufactured. The card provider may optionally set the status of the smart card as inactive to prevent unauthorized use before the intended user can enroll a fingerprint template and contact the card provider to activate the card. 
     In step  2318 , the card provider provides the smart card and a low-cost, simple power source to the user, e.g., sent by mail or courier or given out by a bank or retail outlet. The power source may be battery powered, powered by mains (e.g., via a USB connector), or solar powered. A non-limiting exemplary embodiment of the power source is described in  FIGS. 9A-9H . In some embodiments, if the smart card contains an on-board power source, such as a solar cell, an external power source is not required. 
     In step  2320 , the user connects the smart card to the power source by, for example, inserting the card into a power source housing having contacts for connecting one or more power transmission contacts of the smart card to the power source without connecting any data transmission contacts of the smart card to a device configured to transmit data to or receive data from the card. Accordingly, connecting the smart card to the power source does nothing but provide power to the electrical components of the smart card—e.g., LED, logic elements, sensor elements, etc.—and the power source is unable to transmit data to or from the smart card. 
     The smart card and the power source may be sent to the user with the smart card already inserted in the power source as described in  FIG. 9A . In such embodiments, a battery connection tab is inserted between the power source and the smart card to keep a power connection disconnected. The user may pull out the battery connection tab, as shown in  FIG. 12A , to connect the power source to the smart card. 
     In step  2322  one or more trigger events are detected that results in the fingerprint sensor being put into enrollment mode. An example trigger event may be based on the non-expiration of a timer or a counter. For example, the trigger event may be detecting that the timer or counter has not expired. In such embodiments, a user can enroll a biometric template within a certain time after the fingerprint sensor is put into enrollment mode. In other embodiments, the trigger event may be detecting that the age of the smart card is under a certain age limit which is tracked, for example, by the timer or the counter. The counter may be incremented each time a biometric template has been successfully enrolled or whenever the smart card was used. In such embodiments, the trigger event may be detecting that the counter has not exceeded a predetermined threshold (e.g., a predetermined number of biometric template enrollments or card uses). 
     Another example trigger event may include an occurrence of an error state. A software or hardware component error may occur during the enrollment. An error recovery procedure initiated in response to such software or hardware component error may be the trigger event. In such embodiments, the software or hardware component error would have to be a recoverable error (e.g., a minor error, a transient event or a glitch). Thus, detection of a recoverable error that precluded completion of the enrollment process would cause the sensor to enter enrollment mode. In such embodiments, a non-recoverable error occurring during the enrollment (e.g., a component on the card fails) would not initiate or constitute a trigger event. 
     Other example trigger events include detection of a flag set last time the card was inserted in a card reader (for example a flag set when the card is inserted into a card reader that transmits data to or from the card and instructing the card to enter enrollment mode the next time the card is connected to power), lack of an enrolled fingerprint template on the card is detected, or detecting that power has been provided to the card. Still another trigger event may be detection that the card has been inserted into a power source that has connection to only power contacts on the card and no data transmission contacts. Other events, or combinations of events, may be trigger events. The trigger event may be detected by the fingerprint sensor, or by another component on the card (e.g., the secure element module) or may be detected as a result of the fingerprint sensor and another component on the card interacting, e.g., a handshake. If a component other than the fingerprint sensor detects the trigger event, that component may signal to the fingerprint sensor to enter enrollment mode. 
     The enrollment mode may be triggered, but the user may not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any or sufficient input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     In some embodiments, the card remains in enrollment mode until disconnected from the power source or until the enrollment is complete. If the card is disconnected from the power source before enrollment is complete, the process may move back to step  2322 , whereby an appropriate trigger event will result in the sensor being put back into enrollment mode, or alternatively the user may be required to take some action, such as contact the card provider or obtain a new card, to enable the card to be put into enrollment mode. 
     In some embodiments, the card receives power from the power source, and a status indicator on the smart card (e.g., an LED) indicates to the user that the one or more power transmission contacts of the power source are connected to the power source (i.e., the card is powered), that the fingerprint sensor is in enrollment mode, and the smart card is ready for enrollment to start. 
     In step  2324 , the user can now start to enroll a fingerprint. The fingerprint is enrolled by storing a fingerprint template derived from one or more fingerprint images generated by placing a finger on the fingerprint sensor. The smart card must remain connected to the power source throughout the enrollment process. In the event the smart card is disconnected from the power source during the enrollment process, the enrollment mode in the fingerprint sensor is automatically deactivated. In some embodiments, reconnecting the smart card to the power source moves the process back to step  2322 , whereby an appropriate trigger event will result in the sensor being put back into enrollment mode. The enrollment process is complete when a sufficient fingerprint template is acquired and stored in the fingerprint sensor (e.g., as described in previously incorporated U.S. Pat. No. 9,684,813). Once the enrollment process is complete, enrollment mode in the fingerprint sensor is disabled permanently or alternatively, until a fresh trigger event occurs. In some embodiments, the status indicator provides an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for the fingerprint template and confirm that the enrolling step is successfully complete, e.g., by the LED illuminating for longer period, such as 10 or more seconds. In another embodiment, more than one LED may flash different colors to communicate the various indications described above. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     In step  2326 , the user removes the smart card from the power source, thereby disconnecting the one or more power transmission contacts of the smart card from the power source, and the power source may be discarded. 
     In some embodiments, the card provider sets the status of the card as inactive at step  2316 . In such embodiments, the user must activate the card before attempting to use it. Accordingly, the method  2314  to enroll the biometric template may include a further step  2328  in which the user contacts the card provider (e.g., by phone, app, internet, etc.) to activate the smart card. The user must provide acceptable user verification details to the card provider in order to activate the smart card. If the user is verified, the card provider sets the card status as active in their systems. The user is now able to use the card in the normal way to pay for items, but now requiring fingerprint verification in order to use the smart card. If the user is not verified, the card remains inactive and cannot be used. 
       FIG. 24  is a flowchart illustrating another embodiment of a simple, cost effective method  2400  to enroll a biometric template, such as a fingerprint template, on a device that has limited ability to provide feedback to the user, such as a smart card, is described in detail below. 
     In step  2402 , a data input device, such as an overlay as described in  FIGS. 3B and 13  or a sleeve as described in  FIGS. 10-12 , is temporarily connected to a fingerprint-enabled smart card. In some embodiments, a unique code, such as an activation code, is written into a secure memory of the smart card and encrypted in a secure location during the manufacturing process of the smart card. The fingerprint sensor on the smart card may be calibrated during the manufacturing process and set to data-input mode before the smart card is sent to the user. A data input device, such as, for example any of the overlays or sleeves described herein, may be placed on the card as a final or near-final step of the card manufacturing process. In some embodiments, the data input device is temporarily placed on the card by applying a repositionable adhesive provided by companies such as 3M, Krylon, Franklin Adhesives and Polymers and Bostik may be applied to the overlay  302  to temporarily place over the portion of the card  104  including the sensing area  106 . 
     In step  2404 , the card provider provides the smart card to the user, e.g., sent by mail or courier or given out by a bank or retail outlet. 
     In step  2406 , the user has access to a device, e.g., a smartphone, that is able to provide power wirelessly, e.g., via Near Field Communication, and thus, it is not necessary to provide a power source to the user. A power source may be provided to the user to give the user the choice of using wireless power or wired power. 
     In step  2408 , the user follows instructions, received with the card to obtain an activation code from the card provider. The user may be asked to call a number, or the data input device might have a QR® code that the user can scan with a smart phone, or the user could log-in to their on-line banking site or mobile application and indicate they wish to receive an activation code by SMS. Other secure mechanisms to obtain the activation code may be available in alternative embodiments. In some embodiments, a six digit activation code provides the user with an appropriate security level. The security level may be increased or decreased by varying the number of required digits, depending on the card provider&#39;s requirements. 
     In step  2410 , the user places the smart card near the smartphone in range for NFC connectivity, as shown in  FIGS. 25A-25D . As shown in  FIGS. 25A-25D , the smart card  104  is positioned near a communication device  2502 , such as for example a smart phone, in various configurations. In each configuration, the fingerprint sensor  102  in the smart card  104  is left accessible such that the user can touch the sensing area of the fingerprint sensor  102  while keeping the smart card  104  within the NFC range. The smart card  104  receives power through NFC connectivity and a status indicator on the smart card  104  may show the user that the smart card  104  is ready for enrollment to start. In some embodiments, the user may disable all connectivity on the communication device  2502 , except for NFC, to ensure that the communication device  2502  is completely “off-grid” during the enrollment process for added security. For example, the user can turn off cellular data, Wi-Fi, Bluetooth, etc. 
     Referring back to  FIG. 24 , in step  2412 , the user enters the activation code by sequentially touching the data input keys of the data input device in a sequence corresponding to the activation code, for example, as described in  FIGS. 2A, 3A-3B, 10D, 11A, 12A, 13, 17, 18, 19 and 20 . The fingerprint sensor is configured to simply detect presence of the finger on the remote or direct-contact data input keys in the code entry and unlock mode. In some embodiments, the fingerprint sensor may be configured to detect fingerprint ridges and valleys in the code entry and unlock mode. 
     In some embodiments, the status indicator may indicate to the user that the entered code is correct or incorrect. If the entered code is incorrect, the user may make a pre-determined number of additional attempts before the smart card locks the user out permanently. For example, the user may get three attempts to correctly enter the code. In some embodiments, if the number of unsuccessful attempts reaches the limit or the activation code is not entered before a pre-set time has passed, the smart card may lock the user out permanently. 
     In some embodiments, if one or two unsuccessful entries have been made, the number of unsuccessful entries may be stored in a non-volatile memory. Accordingly, even if power to the smart card is disconnected and reapplied, the smart card may still remember how many unsuccessful entries have been made. Accordingly, the card cannot be “re-set” to a full complement of attempts by disconnecting the card after a number of unsuccessful attempts that is less than the maximum allowed number of attempts. 
     In some embodiments a smart card “state” may be stored in the non-volatile memory of the card. For example, different states may include: (i) “new state” meaning the card is awaiting unlock by entry of a valid activation code; (ii) “unlocked state” meaning that the card is unlocked but enrollment has not been successfully completed; (iii) “active state” meaning that the card is unlocked and an enrollment has been successfully completed; and (iv) “locked state” meaning that the card unlock procedure has been unsuccessfully attempted. 
     In step  2414 , if the activation code has been entered correctly, the user can now remove the data input device from the card and start to enroll a fingerprint (enrollment mode). The smart card must remain in range for NFC connectivity to the smartphone throughout the enrollment process. The status indicator may make an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for a fingerprint template, e.g., by the LED illuminating for longer period, such as 10 or more seconds. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     The user may trigger the enrollment mode by correctly entering the activation code and not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any or sufficient input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     In step  2416 , the user moves the smart card out of range for NFC connectivity to remove the smart card from the power source. In some embodiments, if the user had disabled all connectivity on the device, except for NFC, in step  2410 , the user may re-enable all connectivity on the device. 
     Accordingly, the user has now successfully enrolled a fingerprint in the smart card through method  2400  and can use the smart card in the normal way to pay for items, but now requiring fingerprint verification in order to use the smart card. In some embodiments, multiple users may enroll a fingerprint on the smart card, or a user may enroll multiple fingers on the smart card, using the above noted method. In such embodiments, the card may be programmed with multiple activation codes that are provided to each user. To enroll a new user/finger, a new activation code is entered. 
     In some embodiments of the method  2400  to enroll the biometric template, the data input device may be provided as a sleeve and may guide the user for activation code entry as described in  FIGS. 11A-11C and 12A-12C . 
       FIG. 26A  illustrates a data input device in the form of an overlay which includes data input keys coupled to associated spatially distinct sensing areas on the sensing area of the fingerprint sensor, wherein the data input keys are remotely located from the sensing area according to some embodiments. A portion of the sensing area of the fingerprint sensor is exposed through a cut-out formed in the overlay while another portion of the sensing area is covered by the overlay. 
     As shown in  FIG. 26A , a data input device in the form of an overlay  2602  comprises a portion  2612  covering a portion X (as shown by the dotted lines in  FIG. 26A ) of the sensing area  106  of the fingerprint sensor installed on the smart card  104  and additionally comprises a cut-out  2620  in the overlay  2602  to expose a remaining portion Y of the sensing area  106  of the fingerprint sensor. In a non-limiting exemplary embodiment, a smart card  104  is the device containing the fingerprint sensor, but the application of the data input device is not restricted to a smart card and can be used for any device that contains a fingerprint sensor in alternative embodiments. In some embodiments, the overlay  2602  is removably placed over a portion of the card  104  including portion X of the sensing area  106 , and exposing portion Y of the sensing area through the cutout  2620  of the overlay  2602 . The overlay  2602  includes data input keys  2608 A-D associated with (e.g., coupled to) spatially distinct sensing areas on portion X of the sensing area  106  of the fingerprint sensor. As shown in  FIG. 26A , the data input keys  2608 A-D may be remotely located from the sensing area  106 . 
     The overlay  2602  may comprise a pierced hole  2606  over the LED  308  or other indicator element on the card  104  when the overlay  2602  is placed over a portion of the card  104  including the sensing area  106  and the LED  308 . In some embodiments, an OLED display may operate as the fingerprint sensor. In such embodiments, a portion of the OLED display that is included in portion Y of the sensing area  106  is configured to be used as the indicator element and hence a status indication is visible through the cut-out in the overlay. 
     In some embodiments, each data input key  2608 A-D may function to enable the user to enter numbers (e.g., an activation code, such as a PIN code) by tapping his or her finger on the spatially distinct control areas  2608 A-D. Each data input key  2608 A-D of the overlay  2602  is electrically coupled to an associated spatially distinct portion of portion X of the sensing area  106  such that contact with each key will result in a detectable signal from the sensor element(s) of the associated spatially distinct portion of the sensing area  106 . The coupling between the keys  2608 A-D and the sensing area  106  allows the keys  2608 A-D to be remotely located from the sensing area  106 . This provides the significant advantage of positioning keys  2608 A-D in locations not restricted by the boundaries of the sensing area  106 . For example, extra space on the smart card  104  may be used to provide additional keys (e.g., more than four keys) or the keys  2608 A-D can be spaced further apart, which may improve access for the user. In other embodiments, the overlay  2602  may comprise one data input key electrically coupled to an associated spatially distinct portion of the sensing area  106  configured to receive a Morse code-type data input by the user. 
       FIGS. 26B-26C  illustrate top and bottom surfaces, respectively, of a data input device in the form of an overlay including data input keys coupled to associated spatially distinct sensing areas on the portion X of the sensing area of the fingerprint sensor and additionally including a cut-out to expose the portion Y of the sensing area of the fingerprint sensor according to some embodiments. 
     As shown in  FIGS. 26B-26C , the overlay  2602  comprises a top surface  2604  and a bottom surface  2605 . A portion  2612  of the bottom surface  2605  makes direct contact with the portion X of the sensing area  106  that is smaller than the entire sensing area  106  when the overlay  2602  is placed over the sensing area  106 . In some embodiments, the overlay is made of a non-conductive film, e.g., a thin polymer film and may be less than 100 microns thick. 
     As shown in  FIG. 26B , the top surface  2604  comprises data input keys  2608 A-D, a pierced hole  2606  for an LED  308  (as described above in  FIG. 26A ) or other indicator element on the smart card  104 , an optional tab  2610  for easy removal of the overlay  2602 , and a cut-out area  2620  to expose the portion Y of the sensing area  106  of the fingerprint sensor. The top surface  2604  may be a silk-screen printed to indicate data keys  2608 A-D. The surface of the edge surrounding each data input key  2608 A-D may be slightly raised so that a user may feel the circumference of the holes when placing a finger over it. 
     As shown in  FIG. 26C , the bottom surface  2605  comprises key traces  2614 A-D, connection traces  2616 A-D, sensing area, the pierced hole  2606  for the LED  308  or other indicator element on the smart card  104 , and the cut-out area  2620  to expose the portion Y of the sensing area of the fingerprint sensor. The data input keys  2608 A-D on the top surface align with key traces  2614 A-D on the bottom surface. A conductive material, such as conductive ink, metallization, conductive polymer, or any conductive coating may be used to print or apply the key traces  2614 A-D, the connection traces  2616 A-D, and the sensing area activation traces  2618 A-D onto the bottom surface  2605 . The key traces  2614 A-D are located remotely from the sensing area activation traces  2618 A-D. The connection traces  2616 A-D connect the key traces  2614 A-D to each respective, associated sensing area activation trace  2618 A-D. The sensing area activation traces  2618 A-D are located on the bottom surface  2605  such that the sensing area activation traces  2618 A-D align with associated spatially distinct data input regions of the portion X of the sensing area  106  when the overlay  2602  is placed over the smart card  104 . 
     In a non-limiting exemplary implementation of the embodiment of overlay  2602 , when the fingerprint sensor is in control mode and data input mode, sensor elements within portion  2612  (i.e., portion X) of the sensing area  106  are activated and scanned in contact sensing mode and data input keys  2608 A-D are operatively coupled to associated spatially distinct activation traces  2618 A-D within portion  2612  (i.e., portion X) of the sensing area  106 . When the fingerprint sensor with overlay  2602  is in enrollment mode, only the sensor elements located within portion  2620  (i.e., portion Y) of the two-dimensional array of the sensing area  106  may be activated and scanned in the fingerprint sensing mode, and the sensor controlling circuitry is configured such that multiple images of a user&#39;s fingerprint may be gathered to acquire a sufficient fingerprint template that is stored in memory. In verification or authentication mode, the overlay  2602  would typically have been removed from the card  104  (or other device), and the sensor elements of the entire sensing area, including portion  2612  (i.e., portion X) and portion  2620  (i.e., portion Y), are scanned in fingerprint sensing mode to generate a fingerprint image for comparison against the fingerprint template created in enrollment mode. 
       FIG. 27A  illustrates an embodiment of arranging conductive material over the sensing area of the fingerprint sensor. In this embodiment, the sensing area activation traces  2718 A-D may be in the shape of square or rectangle blocks on portion X  2702  of the sensing area  106 .  FIG. 27A  shows portion X  2702  and portion Y  2704  as two non-overlapping rectangles, sharing one long side along direction “H.” Arranging portion X  2702  and portion Y  2704  in this way optimizes the area of the portion Y  2704 , thereby providing better fingerprint matching performance. However, other implementations are possible, for example, portion X  2702  may be L-shaped or may even form a frame surrounding portion Y  2704 . 
     When the sensing area activation traces  2718 A-D are in the shape of a square or a rectangle block, there may be a loss in detection sensitivity because the sensing area activation traces  2718 A-D are not aligned with the full length of the pickup lines of the sensing area  106 . In order to compensate for any loss in detection sensitivity, the square or rectangle block sensing area activation traces  2718 A-D may be wider along the sensing area length, i.e., direction “H,” than the height in the sensing area width direction “G” in order to cover more pickup lines. In some embodiments, the portion X  2702  of the sensing area  106  covers around 5-20% of the total sensing area  106 . In some embodiments, for a 9 mm×9 mm fingerprint sensor with 6 data input traces, each sensing area activation trace  2718 A-D is approximately 1 mm square, distributed equally along one side of the sensing area  106 . 
       FIG. 27B  illustrates an embodiment of arranging conductive material over the sensing area of the fingerprint sensor including activation traces on a portion of the sensing area connected to data keys and reference traces disposed between and adjacent the activation traces. In some embodiments, sensing area activation traces  2718 A-F of equal size and shape are distributed evenly over portion X  2702  of the sensing area  106 , and reference traces  1502 A-G are distributed evenly between each neighboring pair of the sensing area activation traces  2718 A-F (and adjacent each outer-most activation trace  2718 A and  2718 F) so that the reference traces  1502 A-G align with associated spatially distinct reference regions of portion X  2702  of the sensing area  106 . In some embodiments, reference traces  1502 A-G are the same size and shape as the activation traces  2718 A-F. The sensing area activation traces  2718 A-F are connected through connection traces  1416 A-F to corresponding key traces (not shown). The reference traces  1502 A-G are not connected to the key traces but are subject to noise and unwanted signal inputs similar to that of the sensing area activation trace  2718 A-F. In some embodiments, during the sensor&#39;s scanning process, detected signals from sensor elements covered by the reference traces  1502 A-G (also referred to as reference signals) may be subtracted from detected signals from sensor elements covered the activation traces  2718 A-F (also referred to as activation signals) in order to remove the noise and unwanted signals. In some embodiments, reference signals may be subtracted from activation signals by differential amplifier, as described above in connection with  FIG. 15D . 
       FIG. 27B  illustrates reference traces  1502 A-G and sensor activation traces  2718 A-F that are evenly distributed in portion X  2702  and of equal size and shape. However this is not required and the reference traces  1502 A-G and sensor activation traces  2718 A-F may be of any appropriate size and shape at any appropriate distribution in portion X  2702  in alternative embodiments. 
       FIG. 28  illustrates the data input device in the form of an overlay  2602  temporarily placed over the smart card  104  according to some embodiments. To aid illustration, the upper surface is not shown and the overlay  2602  is shown as transparent, so one can see the bottom surface  2605  in contact with the fingerprint sensor. As shown in  FIG. 28 , the overlay  2602  covers a portion of the smart card  104  containing the sensor area  106 . The overlay  2602  is placed on the smart card  104  such that the sensing area activation traces  2618 A-D on the lower layer  2605  are covering and aligned with the spatially discrete regions of portion X  2702  of sensing area  106  (encompassing one or more specified sensor elements) associated with each key trace  2614 A-D. The cut-out area  2620  in the single layered overlay  2602  leaves portion Y  2704  of sensing area  106  exposed. 
       FIGS. 29A-B  illustrate devices containing fingerprint sensors with data input keys incorporated into the device according to some embodiments. In some embodiments, the data keys are a permanent feature of the device and are not on a temporary overlay. 
       FIG. 29A  shows an example of a smart card  104  according to some embodiments. Smart cards are typically made of multiple layers of plastic, some layers incorporating circuitry and possibly an antenna. In some embodiments, data input keys  2902 A-F may be incorporated into a layer of the card body itself, and portion Y  2704  of the sensing area of the fingerprint sensor  102  may be exposed at a top surface of the card body. In a lower layer, key traces may be coupled with the data input keys  2902 A-F on the upper layer. Connection traces (not shown) connect the key traces to portion X  2702  of the sensing area of the fingerprint sensor  102 . In some embodiments, the data input keys  2902 A-F are partially milled out of the card body to reduce the thickness of the card body between the key and the underlying key trace. The partial milling out of the card body may aid the user to locate the data input keys by touch. 
       FIG. 29B  shows an example of a device such as a smart watch or fitness monitor, according to some embodiments. However, the principles applied to the device described in  FIG. 29B  are not restricted to the smart watch or fitness monitor, and the principles also apply to other devices with limited user interfaces such as key fobs, remote controls, dashboards, white goods, and industrial equipment in alternative embodiments. As shown in  FIG. 29B , data input keys  2902 G-H, and portion Y  2704  of the sensing area of the fingerprint sensor are permanently available to the user on the upper surface of the device. In a layer underneath, key traces may be coupled with the data input keys  2902 G-H. As described above in  FIG. 29A , connection traces (not shown) connect the key traces to portion X  2702  of the sensing area of the fingerprint sensor. 
     Unlike existing smart cards or goods incorporating keypads, the embodiments described in  FIGS. 29A and 29B  offer the manufacturer the opportunity to reduce component costs by using the fingerprint sensor to implement the keypad in addition to offering biometric services. In the specific case of a contactless smartcard containing a fingerprint sensor and data input keys, the embodiment described in  FIG. 29A  may be particularly advantageous in saving on additional circuity and processing logic. In contactless smart cards, the fingerprint sensor  102 , functioning alone, or in conjunction with other components on the card  104 , may be able to harvest power from an NFC signal in order to provide fingerprint authentication when placed in range of a wireless power device according to some embodiments. In such embodiments, the same power harvesting circuitry and power management processing capabilities that the contactless smart card already uses for fingerprint authentication purposes may be employed to power the card wirelessly when data input is required. 
     In a non-limiting exemplary implementation of the embodiment of the smart card of  FIG. 29A  or the device of  FIG. 29B , when the fingerprint sensor  102  is in control mode and data input mode, sensor elements within data input sensing area X  2702  of the sensing area  106  are activated and scanned in contact sensing mode and data input keys are operatively coupled to associated spatially distinct sensor elements within data input sensing area X of the sensing area. When the fingerprint sensor  102  is in enrollment mode, only the sensor elements located within exposed sensing area Y  2704  of the two-dimensional array of the sensing area  106  may be activated and scanned in the fingerprint sensing mode, and the sensor controlling circuitry is configured such that multiple images of a user&#39;s fingerprint may be gathered to acquire a sufficient fingerprint template that is stored in memory. In verification or authentication mode, only the sensor elements located within exposed sensing area Y  2704  of the two-dimensional array of the sensing area  106  may be activated and scanned in the fingerprint sensing mode, and the sensor controlling circuitry is configured to generate a fingerprint image for comparison against the fingerprint template created in enrollment mode. 
     As described above, the sensing area  106  of the fingerprint sensor  102  installed on the device  104  may be selectively configured to operate in five modes: (1) enrollment mode; (2) verification mode; (3) data input mode; (4) control mode; and (5) unlock mode. In some embodiments, the user can select the different modes by different interactions with the sensor  102 , such as a double tap, hold, up/down drag, and left/right drag on the sensor area  106 . In other embodiments, the sensor  102  can be selectively configured in different modes when the user presses the data input keys that are coupled to the sensing area  106 . 
     However, the embodiments shown in  FIGS. 26A and 29A-29B  additionally offer the user the ability to operate in more than one mode simultaneously. For example, if the user was to put one enrolled finger on sensor area Y  2620 ,  2704  and at the same time, press one or more data input keys, the fingerprint sensor can capture a single image from the sensor that would detect the fingerprint image (in area Y  2620 ,  2704 ) and would detect which data input key(s) had been pressed (in area X  2612 ,  2702 ) at that instant. This offers a new suite of possibilities to be able to interact with a host device in a secure fashion since it allows the host device owner to verify their identity at the exact instant the owner is making an additional input. Some examples of how this feature may be used are, for example, the host device can only be locked/unlocked/reset if the verified user of the device is detected when the lock/unlock/reset key is pressed, or certain features on the host device can only be activated if the user is verified at the same time as they press a certain key, or a payment from the user&#39;s account can only be taken if the user is verified at the same time as they press “enter” to authorize the payment, and so on. The features also prevent accidental data entry, e.g., if a user&#39;s biometrically-enabled key fob is in her handbag, if something in the bag presses against the key fob and hits the unlock button, the car won&#39;t unlock because her fingerprint has not been simultaneously detected. 
       FIGS. 30-31  show flow charts describing an enrollment process  3000  and  3100 , respectively, where portion Y  2620  of the sensing area  106  of the fingerprint sensor  102  is exposed to the user through a data input device in the form of an overlay constructed as described in  FIGS. 26B-26C . Since portion Y  2620  of the sensing area  106  is exposed, after the activation code (PIN) has been entered, the user need not remove the overlay until after the user has enrolled his or her finger, or optionally, the user may leave the overlay on the device. 
     Referring to  FIG. 30 , in step  3002 , a data input device, such as a data input device as shown in  FIGS. 26B-26C  is temporarily connected to a biometric-enabled device, such as a fingerprint-enabled smart card. In some embodiments, a unique code, such as an activation code, is written into a secure memory of the smart card and encrypted in a secure location during the manufacturing process of the smart card. The fingerprint sensor on the smart card may be calibrated during the manufacturing process and set to data-input mode before the smart card is sent to the user. 
     In step  3004 , the card provider provides the smart card and a low-cost, simple power source to the user, e.g., sent by mail or courier or given out by a bank or retail outlet. The power source may be battery powered, powered by mains (e.g., via a USB connector), or solar powered. A non-limiting exemplary embodiment of the power source is described in  FIGS. 9A-H . In some embodiments, if the smart card contains an on-board power source, the power source need not be provided to the user. 
     The smart card and the power source may be sent to the user with the smart card already inserted in the power source as described in  FIGS. 11A-11C and 12A-12C . In such embodiments, a battery connection tab is inserted between the power source and the smart card to keep a power connection disconnected. The user may pull out the battery connection tab, as shown in  FIG. 12A , to connect the power source to the smart card. 
     In step  3006 , the user follows instructions, received with the card to obtain an activation code from the card provider. For example, the user could be asked to call a number, or the data input device might have a QR® code that the user can scan with a smart phone, or the user could log-in to their on-line banking site or mobile application and indicate they wish to receive an activation code by SMS. Other secure mechanisms to obtain the activation code may be available in alternative embodiments. A six digit activation code may provide the user with an appropriate security level. The security level may be increased or decreased by varying the number of required digits, depending on the card provider&#39;s requirements. 
     In step  3008 , if not already done, the user connects the smart card to the power source, for example by inserting the card into a power source housing. The card receives power from the power source, and a status indicator on the smart card (e.g., an LED) may indicate to the user that the smart card is ready. 
     In step  3010 , the user enters the activation code by sequentially touching the data input keys of the data input device in a sequence corresponding to the activation code. The status indicator can indicate to the user that the entered code is correct or incorrect. As described above, if the entered code is incorrect, the user can make a pre-determined number of additional attempts before the smart card locks the user out permanently. For example, the user may get three attempts to correctly enter the code. In some embodiments, if the number of unsuccessful attempts reaches the limit or the activation code is not entered before a pre-set time has passed, the smart card locks the user out. 
     In step  3012 , if the activation code has been entered correctly, the user can now start to enroll a fingerprint (enrollment mode) without removing the data input device from the card. The smart card must remain connected to the power source throughout the enrollment process. In some embodiments, the status indicator makes an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for a fingerprint template, e.g., by the LED illuminating for longer period, such as 10 or more seconds. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     The user may trigger the enrollment mode by correctly entering the activation code and not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any or sufficient input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     In step  3014 , the user removes the smart card from the power source, and the power source may be discarded. The user may, optionally, also remove the data input device after successful enrollment, possibly after additional data input. 
     Accordingly, the user has now successfully enrolled a fingerprint in the smart card through the enrollment process  3000  and can use the smart card in the normal way to pay for items, but now requiring fingerprint verification in order to use the smart card. In some embodiments, multiple users may enroll a fingerprint on the smart card, or a user may enroll multiple fingers on the smart card, using the above noted process  3000 . In such embodiments, the card may be programmed with multiple activation codes that are provided to each user. To enroll a new user/finger through the enrollment process  3000 , a new activation code is entered, which is made convenient by the fact that the data input device was not removed during enrollment of the previous fingerprint. 
     Referring to  FIG. 31 , in step  3102 , a data input device, such as a data input device as shown in  FIGS. 26A-26C  is temporarily connected to a biometric-enabled device, such as a fingerprint-enabled smart card. In some embodiments, a unique code, such as an activation code, is written into a secure memory of the smart card and encrypted in a secure location during the manufacturing process of the smart card. 
     In step  3104 , the card provider provides the smart card to the user, e.g., sent by mail or courier or given out by a bank or retail outlet. 
     In step  3106 , the user has access to a device, e.g., a smartphone, that is able to provide power wirelessly, e.g., via Near Field Communication, and thus, it is not necessary to provide a power source to the user. A power source may optionally be provided to the user to give the user the choice of using wireless power or wired power. 
     In step  3108 , the user follows instructions, received with the card to obtain an activation code from the card provider. For example, the user could be asked to call a number, or the data input device might have a QR® code that the user can scan with a smart phone, or the user could log-in to their on-line banking site or mobile application and indicate they wish to receive an activation code by SMS. Other secure mechanisms to obtain the activation code may be available in alternative embodiments. A six digit activation code may provide the user with an appropriate security level. The security level may be increased or decreased by varying the number of required digits, depending on the card provider&#39;s requirements. 
     In step  3110 , the user places the smart card near the smartphone in range for NFC connectivity, e.g., as shown in  FIGS. 25A-25D . The smart card receives power through NFC connectivity and a status indicator shows the user that the smart card is ready for enrollment to start. In an embodiment, the user could disable all connectivity on the device, except for NFC, to ensure that the device is completely “off-grid” during the enrollment process for added security. For example, the user can turn off cellular data, Wi-Fi, Bluetooth, etc. 
     In step  3112 , the user enters the activation code by sequentially touching the data input keys of the data input device in a sequence corresponding to the activation code. The status indicator may indicate to the user that the entered code is correct or incorrect. If the entered code is incorrect, the user may make a pre-determined number of additional attempts before the smart card locks the user out permanently. For example, the user may get three attempts to correctly enter the code. In some embodiments, if the number of unsuccessful attempts reaches the limit or the activation code is not entered before a pre-set time has passed, the smart card locks the user out. 
     In some embodiments, if one or two unsuccessful entries have been made, the number of unsuccessful entries is stored in a non-volatile memory. Accordingly, even if power to the smart card is disconnected and reapplied, the smart card still remembers how many unsuccessful entries have been made. Accordingly, the card cannot be “re-set” to a full complement of attempts by disconnecting the card after a number of unsuccessful attempts that is less than the maximum allowed number of attempts. 
     In step  3114 , if the activation code has been entered correctly, the user can now start to enroll a fingerprint (enrollment mode) without removing the data input device from the card. The smart card must remain in range for NFC connectivity to the smartphone throughout the enrollment process. In some embodiments, the status indicator may make an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for a fingerprint template, e.g., by the LED illuminating for longer period, such as 10 or more seconds. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     The user may trigger the enrollment mode by correctly entering the activation code and not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any or sufficient input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     In step  3116 , the user moves the smart card out of range for NFC connectivity to remove the smart card from the power source and optionally removes the data input device. In some embodiments, if the user had disabled all connectivity on the device, except for NFC, in step  3110 , the user can re-enable all connectivity on the device. 
       FIGS. 32-33  are flow charts showing enrollment process  3200  and  3300 , respectively, on a device as illustrated in  FIGS. 29A-B  where data input keys  2902 A-F,  2902 G-H and portion Y  2704  of the fingerprint sensor  102  are permanently available to the user. 
     Referring to  FIG. 32 , in step  3202 , data input keys are incorporated into a fingerprint-enabled smart card or other device. In some embodiments, a unique code, such as an activation code, is written into a secure memory of the device and encrypted in a secure location during the manufacturing process of the device. The fingerprint sensor on the device may be calibrated during the manufacturing process and set to data-input mode before the smart card is sent to the user. 
     In step  3204 , the device provider provides the device and a low-cost, simple power source to the user, e.g., sent by mail or courier or given out by a bank or retail outlet. The power source may be battery powered, powered by mains (e.g., via a USB connector), or solar powered. A non-limiting exemplary embodiment of the power source is described in  FIGS. 9A-9H . In some embodiments, if the device contains an on-board power source, the power source need not be provided to the user. 
     A smart card and the power source may be sent to the user with the smart card already inserted in the power source as described in  FIGS. 11A-11C and 12A -C. In such embodiments, a battery connection tab is inserted between the power source and the smart card to keep a power connection disconnected. The user may pull out the battery connection tab, as shown in  FIG. 12A , to connect the power source to the smart card. 
     In step  3206 , the user follows instructions, received with the device to obtain an activation code from the device provider. For example, the user could be asked to call a number, or the data input device might have a QR® code that the user can scan with a smart phone, or the user could log-in to their on-line banking site or mobile application and indicate they wish to receive an activation code by SMS. Other secure mechanisms to obtain the activation code may be available in alternative embodiments. A six digit activation code may provide the user with an appropriate security level. The security level may be increased or decreased by varying the number of required digits, depending on the card provider&#39;s requirements. 
     In step  3208 , if not already done, the user connects the device to the power source, for example by inserting the device, e.g., a card, into a power source housing. The device receives power from the power source, and a status indicator on the device (e.g., an LED) indicates to the user that the device is ready. 
     In step  3210 , the user enters the activation code by sequentially touching the data input keys of the data input device in a sequence corresponding to the activation code. The status indicator may indicate to the user that the entered code is correct or incorrect. As described above, if the entered code is incorrect, the user may make a pre-determined number of additional attempts before the smart card locks the user out permanently. For example, the user may get three attempts to correctly enter the code. In some embodiments, if the number of unsuccessful attempts reaches the limit or the activation code is not entered before a pre-set time has passed, the smart card locks the user out. 
     In step  3212 , if the activation code has been entered correctly, the user can now start to enroll a fingerprint (enrollment mode). The device must remain connected to the power source throughout the enrollment process. The status indicator may make an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for a fingerprint template, e.g., by the LED illuminating for longer period, such as 10 or more seconds. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     The user may trigger the enrollment mode by correctly entering the activation code and not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any or sufficient input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     In step  3214 , the user removes the device from the power source. 
     Accordingly, the user has now successfully enrolled a fingerprint in the device according to process  3200  and can use the device in the normal way, but now requiring fingerprint verification in order to use the device. In some embodiments, multiple users may enroll a fingerprint on the device, or a user may enroll multiple fingers on the device, using the above noted method. In such embodiments, the device may be programmed with multiple activation codes that are provided to each user. To enroll a new user/finger according to process  3200 , a new activation code is entered, which is made convenient by the fact that the data input keys are permanently incorporated into the device. 
     Referring to  FIG. 33 , the process  3300  begins with step  3302 , in which data input keys are incorporated into a fingerprint-enabled smart card or other device. In some embodiments, a unique code, such as an activation code, is written into a secure memory of the device and encrypted in a secure location during the manufacturing process of the device. The fingerprint sensor on the device may be calibrated during the manufacturing process and set to data-input mode before the smart card is sent to the user. 
     In step  3304 , the device provider provides the device to the user, e.g., sent by mail or courier or given out by a bank or retail outlet. 
     In step  3306 , the user has access to a device, e.g., a smartphone, that is able to provide power wirelessly, e.g., via Near Field Communication, and thus, it is not necessary to provide a power source to the user. A power source may be provided to the user to give the user the choice of using wireless power or wired power. 
     In step  3308 , the user follows instructions, received with the device to obtain an activation code from the device provider. For example, the user could be asked to call a number, or be given a QR® code that the user can scan with a smart phone, or the user could log-in to their on-line banking site or mobile application and indicate they wish to receive an activation code by SMS. Other secure mechanisms to obtain the activation code may be available in alternative embodiments. A six digit activation code may provide the user with an appropriate security level. The security level may be increased or decreased by varying the number of required digits, depending on the card provider&#39;s requirements. 
     In step  3310 , the user places the device near the smartphone in range for NFC connectivity, e.g., as shown in  FIGS. 25A-25D . The device receives power through NFC connectivity and a status indicator shows the user that the smart card is ready for enrollment to start. In some embodiments, the user may disable all connectivity on the device, except for NFC, to ensure that the device is completely “off-grid” during the enrollment process for added security. For example, the user can turn off cellular data, Wi-Fi, Bluetooth, etc. 
     In step  3312 , the user enters the activation code by sequentially touching the data input keys in a sequence corresponding to the activation code. The status indicator may indicate to the user that the entered code is correct or incorrect. If the entered code is incorrect, the user may make a pre-determined number of additional attempts before the smart card locks the user out permanently. For example, the user may get three attempts to correctly enter the code. In some embodiments, if the number of unsuccessful attempts reaches the limit or the activation code is not entered before a pre-set time has passed, the smart card locks the user out. 
     The user may trigger the enrollment mode by correctly entering the activation code and not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any or sufficient input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     In some embodiments, if one or two unsuccessful entries have been made, the number of unsuccessful entries is stored in a non-volatile memory. In such embodiments, even if power to the smart card is disconnected and reapplied, the smart card still remembers how many unsuccessful entries have been made. Accordingly, the card cannot be “re-set” to a full complement of attempts by disconnecting the card after a number of unsuccessful attempts that is less than the maximum allowed number of attempts. 
     In step  3314 , if the activation code has been entered correctly, the user can now start to enroll a fingerprint (enrollment mode). The device must remain in range for NFC connectivity to the smartphone throughout the enrollment process. In some embodiments, the status indicator makes an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for a fingerprint template, e.g., by the LED illuminating for longer period, such as 10 or more seconds. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     In step  3316 , the user moves the device out of range for NFC connectivity to remove the smart card from the power source. In some embodiments, if the user had disabled all connectivity on the device, except for NFC, in step  3310 , the user can re-enable all connectivity on the device. 
       FIGS. 34A-34E  illustrate another embodiment of a data input device in the form of an overlay  3402 . As shown in  FIGS. 34A-34E , the overlay  3402  integrates a power source (also referred to as a non-data-transmitting power source) for the fingerprint sensor  102  installed on a device  104  as well as data input elements for entering data via signals generated at the fingerprint sensor. In the embodiment described in relation to  FIGS. 34A-34E , a smart card is the device containing the fingerprint sensor. However, the application of the data input device is not restricted to a smart card and can be used for any device that contains a fingerprint sensor in alternative embodiments. In some embodiments, the smart card  104  comprises the fingerprint sensor  102  with a sensing area  106 , possibly LEDs or other status indicators  308 , and contact pads  108  providing contacts for an external power source. 
     In some embodiments, the overlay  3402  comprises a thin material, e.g., a film that conforms to a surface of the host device when secured thereto. The overlay  3402  may comprise an adhesively-backed sticker or film temporarily and removably placed over the card. In some embodiments, repositionable adhesives provided by companies such as 3M, Krylon, Franklin Adhesives and Polymers, and Bostik may be applied to the overlay  3402  to temporarily place over the portion of the card  104  including the contact pads  108 . In other embodiments, the temporary overlay  3402  may be slid over the device, clipped onto the device, or folded onto the device rather than adhering to the device surface. The overlay may be magnetic and stick to the device surface if the device is metal. 
       FIG. 34A  is a plan view of an embodiment of a data input device in the form of an overlay  3402  integrating a power source with a host device (e.g., smart card) disposed beneath the overlay. Features disposed on the back, or non-exposed surface, of the overlay  3402  or features disposed on the underlying host device that are covered by the overlay  3402  are shown in dashed lines in  FIGS. 34A, 34B, and 34F . The overlay  3402  is configured to provide power to an electronic device  104 , such as a smart card, having terminals (e.g., power connection pads) for connecting a source of electric power to the electronic device  104 , and the overlay  3402  is configured to be removably secured to a surface of the electronic device  104 . 
     In some embodiments, the overlay  3402  is not secured to the surface of the device  104 , but is connected to the device  104  by a ribbon cable or other conductor. For example, a power source, such as that shown in  FIGS. 34A-34F and 35 , may be incorporated in a remote keypad device  1902  shown in  FIG. 19 , and data transfer cable  1906  may also include conductive contacts for connecting the power source to power transmission pads of the host device  104 . 
     The overlay  3402  may comprise a suitable power element  3404  to power the card  104 , such as a small cell battery LR44. In such embodiments, the power element  3404  is securely attached to the overlay  3402  and makes electrical contact with power element contact pad  3406 . For example, one terminal of a battery may contact the power element contact pad  3406 . As shown in  FIG. 34A , the power element contact pad  3406  makes contact with power connection trace  3410 A. A corresponding conductive contact  3408  is printed or etched onto a section of the overlay  3402  which can be folded such that the conductive contact  3408  aligns with the power element  3404 . In some embodiments, pressure applied to the folded conductive contact  3408  holds the conductive contact  3408  in contact with the power element  3404 . For example, the conductive contact  3408  contacts another terminal of the battery. The surface of conductive contact  3408  may be coated in conductive, repositionable adhesive such that the folded section of overlay will stay in contact with the power element  3404  without the user having to continue to hold it in place. Conductive contact  3408  additionally makes contact with power connection trace  3410 B. 
     In some embodiments, power connection traces  3410 A and  3410 B are printed in conductive ink or are etched on the overlay  3402 . Power connection trace  3410 A routes the power element  3404  and power element contact pad  3406  to the ground connection  3414  on contact pad  108 . Power connection trace  3410 B routes the conductive contact  3408  to the card contact power input on contact pads  108  on the smart card  104 . Moving the conductive contact  3408  into contact with power element  3404  (i.e., so that conductive contact  3408  contacts one part (e.g., terminal) of the power element  3404  and the power element contact pad  3406  contacts another part (e.g., terminal) of the power element  3404 ) completes a circuit from the conductive contact  3408 , through the power element  3404 , and to the power element contact pad  3406 . The overlay  3402  includes a circuit closure configured to enable a user to selectively close a power circuit between the power element  3404  and the terminals of the electronic device to enable power transmission between the power element and the electronic device. In some embodiments, the circuit closure includes a section of the overlay  3402  containing conductive contact  3408  folded (e.g., over a fold line  3407  shown in  FIG. 34A ) such that when the conductive contact  3408  makes contact with power element  3404  the power source circuit is completed and power is supplied to the card  104 . The conductive contact  3408  may be held in contact with the power element  3404  by applying pressure to the conductive contact  3408 . For example, the pressure may be applied by a user&#39;s press or pinch, by a conductive adhesive between the conductive contact  3408  and the power element  3404  or by mechanical means, such as a clip or clasp. 
     The overlay  3402  may include data input keys  2608 A-F, connection traces  2616 A-F coupling each data input key with an associated, spatially distinct portion (part of portion X  3401 ) of the sensing area  106  of the fingerprint sensor, and a cutout  2620  exposing a portion Y  3403  of the sensing area  106  as described above. 
       FIG. 34B  is a view of the overlay  3402  and host device with a portion of the overlay folded over to complete a power circuit to the host device according to some embodiments. 
       FIG. 34B  shows the result of folding a section of the overlay  3402  to align the conductive contact  3408  and power element  3404  to complete the power source circuit and provide power to the card  104 . In some embodiments, status indicators  308 , e.g., light elements (e.g., LEDs) and/or other visual or auditory elements, may be used to signal to the user that power is present and/or that the enrollment process may begin. 
     In some embodiments the overlay  3402  may be transparent or translucent such that one can see its various elements and their alignment with associated elements of the smart card  104 . However, this is not required and the overlay may not be transparent or translucent in alternative embodiments. 
       FIG. 34C  is a plan view illustrating a surface of overlay  3402  that is placed in contact with the card  104  according to some embodiments. The card  104  and the power element  3404  are not shown in  FIG. 34C . The surface of the overlay  3402  shown in  FIG. 34C  makes contact with the surface of the card  104  and includes the power connection traces  3410 A,  3410 B and card contacts  3412 ,  3414  that contact power pads (e.g., power terminals) of the contact pads  108  when the overlay  3402  is applied to the card  104 .  FIG. 34D  is a plan view illustrating a card  104  placed on the overlay  3402  according to some embodiments. In some embodiments, the overlay  3402  includes a rectangular portion having a size (e.g., length and width) and shape generally corresponding to the size and shape of the card  104 , and the overlay  3402  is placed on the card  104  with three edges defining three sides of the rectangular portion aligned with the three corresponding edges of the card  104  to help ensure that the overlay  3402  is properly positioned with respect to the card  104  such that power contacts  3412 ,  3414  of the overlay  3402  align with the proper pads of the pads  108  of the card  104  and such that the cutout  2620  properly aligns with the sensing area  106  of the card  104 . 
     In a non-limiting exemplary implementation of the embodiment of the overlay  3402 , when the fingerprint sensor is in control mode and data input mode, sensor elements within a portion (portion X  3401 ) of the sensing area  106  covered by the overlay  3402  are activated and scanned in contact sensing mode and data input keys  2608 A-D are operatively coupled to associated spatially distinct activation traces within the portion X  3401  of the sensing area  106  that is covered by part of the overlay  3402 . When the fingerprint sensor with overlay  3402  is in enrollment mode, only the sensor elements located within the portion Y  3403  of the two-dimensional array of the sensing area  106  exposed by cutout  2620  may be activated and scanned in the fingerprint sensing mode, and the sensor controlling circuitry is configured so that multiple images of a user&#39;s fingerprint may be gathered to acquire a sufficient fingerprint template that is stored in memory. In verification or authentication mode, the overlay  3402  would typically have been removed from the card  104  (or other host device in alternative embodiments), and the sensor elements of the entire sensing area  106 , including the portion X  3401  and the portion Y  3403 , are scanned in fingerprint sensing mode to generate a fingerprint image for comparison against the fingerprint template created in enrollment mode. 
       FIG. 34E  is a plan view of an upper surface of overlay  3402  (i.e., the surface not in contact with the smart card) according to some embodiments. The user may make contact with the surface shown in  FIG. 34E  when the overlay  3402  is applied to the card  104 . 
     In some embodiments of the overlay  3402 , the power element may be a USB socket. In such embodiments, the USB socket may be connected to the power and ground inputs of the contact pads  108  via power connection traces  3410 A and  3410 B. The circuit closure may be established by inserting a USB cable into the socket and connecting the overlay  3402  to the mains. 
     In some embodiments of the overlay  3402 , the power element may be a solar cell with a pull tab cover. In such embodiments, the solar cell may be connected to the power and ground inputs of the contact pads  108  via power connection traces  3410 A and  3410 B. The circuit closure may be established by removing the pull tab covering the solar cell, thus exposing it to light. 
     In some embodiments of the overlay  3402 , the power element may be an NFC transceiver, mounted on the overlay  3402 . In such embodiments, the NFC transceiver may be connected to the power and ground inputs of the contact pads  108  via power connection traces  3410 A and  3410 B and is able to harvest power from a NFC-enabled device such as a mobile phone or card reader. The circuit closure may be established by placing the card  104  within range of the NFC-enabled device and keeping it in range until the desired process completes. 
     As shown in  FIGS. 34A and 34C , the overlay  3402  may further comprise a portion  2612  covering the portion X  3401  of the sensing area  106  of the fingerprint sensor installed on the smart card  104 , and a cut-out  2620  in the overlay  3402  to expose the remaining portion Y  3403  of the sensing area  106  of the fingerprint sensor. The overlay  3402  includes data input keys  2608 A-F associated with (e.g., coupled to) spatially distinct sensing areas on the portion X  3401  of the sensing area  106  of the fingerprint sensor by connection traces  2616 A-F. The data input keys  2608 A-F may be remotely located from the sensing area  106 . 
     In some embodiments, as described above, each data input key  2608 A-F may function to enable the user to enter numbers (e.g., an activation code, such as a PIN code) by touching a data input key  2608 A-F with a finger. Each data input key  2608 A-F of the overlay  3402  is electrically coupled to an associated spatially distinct portion of the portion X  3401  of the sensing area  106  such that contact with each key will result in a detectable signal from the sensor element(s) of the associated spatially distinct portion of the sensing area  106 . The coupling between the keys  2608 A-F and the sensing area  106  allows the keys  2608 A-F to be remotely located from the sensing area  106 . This provides the significant advantage of positioning keys  2608 A-F in locations not restricted by the boundaries of the sensing area  106 . For example, extra space on the smart card  104  may be used to provide additional keys (e.g., more than four keys) or the keys  2608 A-F can be spaced further apart, which may improve access for the user. The overlay  3402  may comprise one data input key electrically coupled to an associated spatially distinct portion of the sensing area  106  configured to receive a Morse code-type data input by the user. 
     The overlay  3402  may comprise a portion that covers the fingerprint sensor installed on the smart card  104 , but additionally including data input keys associated with (e.g., coupled to) spatially distinct sensing areas on the sensing area  106  of the fingerprint sensor where the data input keys are located on the sensing area  106 , as shown in  FIG. 3B , or where the data input keys are remotely located from the sensing area  106  as shown in  FIG. 13 . In both of these scenarios, the portion of the overlay  3402  covering the fingerprint sensor may be separable from the section of the overlay  3402  comprising the power source connected to the power inputs of the smart card  104 . For example, the overlay  3402  may be in two parts, or is perforated, or the overlay has two layers—one on top of the other—where the section containing the data input keys is uppermost. Thus, after the user has entered data using the data input keys, the fingerprint sensor can be revealed to complete the enrollment, without disrupting the power supply to the card  104 . When enrollment is complete, the remaining portion of the overlay  3402  may be removed. 
     In some embodiments, an overlay  3402 F, as shown in  FIG. 34F , does not cover the sensing area  106  or fingerprint sensor  102  of the host device  104 . Rather, the overlay  3402 F simply covers the portion of the card  104  including the contact pads  108 . The overlay  3402 F may comprise a power element  3404  disposed on a power element contact pad  3406 , a conductive contact  3408 , a power connection trace  3410 A connecting the power element contact pad  3406  to card contact ground  3414 , which is connected to a power contact pad of the contact pads  108 , and power connection trace  3410 B connecting the conductive contact  3408  to card contact power input  3412 , which is connected to another power contact pad of the contact pads  108 . In some embodiments, the overlay  3402 F is strictly a power source for a smart card  104  or other device and does not include data input functionality. The overlay  3402 F may be used in combination with data input devices, such as those shown in  FIGS. 3B, 13, and 26A-26C  and discussed herein. 
     The data input device in the form of an overlay  3402  may comprise a pierced hole  2606  over the LED  308  or other indicator element on the card  104  when the overlay  3402  is placed over a portion of the card  104  including the sensing area  106  and the LED  308 . In other embodiments, an OLED display may operate as the fingerprint sensor. In such embodiments, a portion of the OLED display that is included in portion Y  3403  of the sensing area  106  may be configured to be used as the indicator element and hence a status indication is visible through the cut-out  2620  in the overlay  3402 . 
     The overlay  3402  may comprise one or more LEDs or other status indicators (e.g., visual, audible, tactile indicators) used to indicate the status to the user during enrollment in a situation where there are no status indicators on the smart card itself, where status indicators on the smart card are not suitable, or to supplement the status indicators on the smart card. In such embodiments, a component on the smart card  104 , such as the fingerprint sensor, the secure element module, or other processing circuitry, monitors the state of the enrollment process and modulates a power line in the card  104  in a known manner, depending on the state of the enrollment process. The overlay  3402  may further comprise a detector circuit configured to detect the power line modulation and activate the one or more LEDs accordingly to indicate the correct state of the enrollment process. 
       FIG. 35  illustrates an embodiment of a power source overlay (also referred to as a non-data-transmitting power source)  3502  according to some embodiments. As shown in  FIG. 35 , the power source overlay  3502  comprises a power element  3504  for the fingerprint sensor  102  installed on a device  104 . In the illustrated embodiment shown in  FIG. 35 , a smart card is the device containing the fingerprint sensor, but the application of the power source overlay  3502  is not restricted to a smart card and can be used for any device that contains a fingerprint sensor in alternative embodiments. The card  104  comprises the fingerprint sensor  102  with a sensing area  106 , LEDs or other status indicators  308 , and contact pads  108  providing contacts for an external power source. 
     In the illustrated embodiment shown in  FIG. 35 , the overlay  3502  is an adhesively-backed sticker or film which may be temporarily and removably placed over the card  104 . In an embodiment, repositionable adhesives provided by companies such as 3M, Krylon, Franklin Adhesives and Polymers, and Bostik may be applied to the overlay  3502  to temporarily place over the portion of the card  104  including the contact pads  108 . In some embodiments, the temporary overlay  3502  may be slid over the device  104 , clipped onto the device  104 , or folded onto the device  104  rather than being adhered to the device surface. The temporary overlay may be magnetic and stick to the device surface if the device is metal. 
     In some embodiments, the overlay  3502  comprises a suitable power element  3504  to power the card  104 , such as a small cell battery LR44. The bottom of the power element  3504  is securely attached to the overlay  3502  and makes contact with power connection trace  3510 B. In some embodiments, one end of a conductive spring clip  3508  contacts the top of the power element  3504  and the other end of the conductive spring clip  3508  connects to power connection trace  3510 A. 
     In some embodiments, power connection traces  3510 A and  3510 B are printed in conductive ink or are etched on the overlay  3502 . The power connection trace  3510 A electrically connects the power element  3504  via the conductive spring clip  3508  to ground connections  3414  on contact pads  108 . The power connection trace  3510 B electrically connects the power element  3504  to the card contact power input  3412  on contact pads  108  on the smart card  104 . The circuit closure includes a pull tab  3506  made of non-conducting material temporarily placed between the power element  3504  and the conductive spring clip  3508  to break the power circuit. When the user removes the pull tab  3506  out of the spring clip  3508 , the power source circuit is completed and power is supplied to the card  104 . In some embodiments, status indicators  308  may be used to signal to the user that power is present and/or that the enrollment process may begin. 
     The overlay  3502  may be coated with conductive material. In such embodiments, power connection traces  3510 A,  3510 B are absent. Instead, the overlay  3502  may be shaped such that that the overlay  3502  couples with the ground connections  3414  on contact pads  108  and with the card contact power input  3412  on contact pads  108  on the smart card  104  and the terminals of the power element do not conductively couple with any other part of contact pad  108 . 
     The overlay  3502  may be part of data input device extending over the fingerprint sensor  102 . Data input keys and associated key traces may be printed and/or etched on the overlay  3502  and coupled to the sensing area  102  in a similar manner as was described for  FIG. 34A-E  to allow the user to input data. In other embodiments, the overlay  3502  may comprise a portion that covers the fingerprint sensor  102  installed on the smart card  104 , and further comprise data input keys associated with (e.g., coupled to) the spatially distinct sensing areas on the sensing area  106  of the fingerprint sensor where the data input keys are located on the sensing area, as shown in as shown in  FIG. 3B , or where the data input keys are remotely located from the sensing area  106  as shown in  FIG. 13 . In both of these scenarios, the portion of the overlay  3502  covering the fingerprint sensor  102  may be separable from the section of the overlay containing the power source connected to the power inputs of the smart card. For example, the overlay  3502  may be in two parts, or is perforated, or the overlay has two layers—one on top of the other—where the section containing the data input keys is uppermost. Thus, after the user has entered data using the data input keys, the fingerprint sensor  102  can be revealed to complete the enrollment, without disrupting the power supply to the card  104 . When enrollment is complete, the remaining portion of the overlay  3502  can be removed. 
     The overlay  3502  may comprise one or more LEDs or other status indicators (e.g., visual, audible, tactile indicators) used to indicate the status to the user during enrollment in a situation where there are no status indicators on the smart card itself, where status indicators on the smart card are not suitable, or to supplement the status indicators on the smart card. In such embodiments, a component on the smart card  104 , such as the fingerprint sensor, secure element module, or other processing circuitry, monitors the state of the enrollment process and modulates a power line in the card  104  in a known manner, depending on the state of the enrollment process. The overlay  3502  may further comprise a detector circuit configured to detect the power line modulation and activate the one or more LEDs accordingly to indicate the correct state of the enrollment process. 
     In an alternative embodiment of  FIGS. 34A-34F  and  FIG. 35 , the circuit closure may comprise a switch or button instead of the folding overlay section of  FIGS. 34A-34F  or the pull tab of  FIG. 35 , thus enabling the user to complete the power circuit by applying the switch or button. 
     In an alternative embodiment of  FIGS. 34A-34F  and  FIG. 35 , the overlay  3402 ,  3502  makes contact with data input and output contacts on the card contact pad  108  in addition to the power input and ground contacts. This may enable the overlay  3402 ,  3502  to provide communication channels to and from elements on the card  104 , such as the secure element module or the biometric sensor. A wireless transceiver (e.g., Bluetooth, WiFi, NFC) mounted to the overlay  3402 ,  3502  and connected to the data input/outputs of the card contact pads  108  may permit elements in the card  104  to wirelessly connect to other devices such as a mobile phone, lap top, ATM, card reader, or PC. The overlay  3402 ,  3502  may harvest power from the wireless signal to power the card  104  in addition to using the wireless connection to provide a communication channel. In such embodiments, the overlay  3402 ,  3502  capable of harvesting power may temporarily convert a contact card into a contactless card. 
     A cable socket (e.g., USB) mounted to the overlay  3402 ,  3502  and connected to the data inputs/outputs of the card contact pads  108  may permit elements in the card  104  to connect via a cable to other devices such as a mobile phone, lap top, ATM, card reader, or PC. The overlay  3402 ,  3502  may also receive power from the cable to power the card in addition to using the cable connection to provide a communication channel. 
     The overlay  3402 ,  3502  may make contact with the data input and output contacts on the card contact pad  108  in addition to the power input and ground contacts. In such embodiments, the overlay  3402 ,  3502  may provide status indications to the user regarding elements on the card  104 , such as the secure element module, the biometric sensor, and external devices connected to the card  104 . For example, LEDs, buzzers, or a small LCD screen mounted on the overlay  3402 ,  3502  and connected to the data input/outputs of the card contact pad  108  may indicate commands, responses, status information, data or instructions to the user. 
       FIG. 36  is a flowchart illustrating an embodiment of a simple, cost effective method  3600  to enroll a biometric template, such as a fingerprint template, on a device that has limited ability to provide feedback to the user, such as a smart card, requiring entry of activation data (i.e., an activation code) prior to enrolling the fingerprint template. 
     In step  3602 , a data input device, such as the overlay described in  FIGS. 34A-34E , is temporarily connected to a biometric-enabled device, such as a fingerprint-enabled smart card. A unique code, such as an activation code, may be stored in a secure memory of the smart card and encrypted in a secure location during the manufacturing process of the smart card. The fingerprint sensor on the smart card may be calibrated during the manufacturing process and set to data-input mode before the smart card is sent to the user. 
     In step  3604 , the card provider provides the smart card and the data input device with integral power source to the user. For example, the card provider may provide the smart card and the data input device with integral power source to the user by mail, courier or directly at a bank or a retail outlet. The card and data input device may be packaged such that the power circuit cannot be completed accidentally during transit. 
     In step  3606 , the user follows instructions to obtain an activation code from the card provider. In some embodiments, the instructions to obtain the activation code may be received with the card. For example, the user may be asked to call a number, the data input device might have a QR® code that the user can scan with a smart phone or the user may log-in to their on-line banking site or mobile application and indicate the user wishes to receive an activation code by SMS. Other secure mechanisms to obtain the activation code may be available in alternative embodiments. A six digit activation code may provide the user with an appropriate security level. The security level may be increased or decreased by varying the number of required digits, depending on the card provider&#39;s requirements. 
     In step  3608 , the user connects the smart card to the power source by completing the power circuit. For example, the power circuit may be completed by folding a section of the data input device to make conductive contact pads meet or by removing a pull tab separating the power source from the smart card. Accordingly, the card receives power from the power source, and a status indicator on the smart card (e.g., an LED) may indicate to the user that the smart card is ready. 
     In step  3610 , the user enters the activation code by sequentially touching the data input keys of the data input device in a sequence corresponding to the activation code. In some embodiments, the status indicator may indicate to the user that the entered code is correct or incorrect. As described herein, if the entered code is incorrect, the user may make a pre-determined number of additional attempts before the smart card locks the user out permanently. For example, the user may get three attempts to correctly enter the code. In some embodiments, if the number of unsuccessful attempts reaches the limit or the activation code is not entered before a pre-set time has passed, the smart card locks the user out. 
     In step  3612 , if the activation code has been entered correctly, the user can now start to enroll a fingerprint (enrollment mode) without removing the data input device from the card. The smart card must remain connected to the power source throughout the enrollment process. The status indicator may make an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for a fingerprint template, e.g., by the LED illuminating for longer period, such as 10 or more seconds. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     The user may trigger the enrollment mode by correctly entering the activation code and not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     In step  3614 , the user removes the data input device from the smart card, and the data template may be discarded. The user may, optionally, also remove the data input device after successful enrollment, possibly after additional data input. 
     Accordingly, the user has now successfully enrolled a fingerprint in the smart card through the simple, cost effective method  3600  and can use the smart card in the normal way to pay for items, but now requiring fingerprint verification in order to use the smart card. In some embodiments, multiple users may enroll a fingerprint on the smart card, or a user may enroll multiple fingers on the smart card, using the above noted method  3600 . In such embodiments, the card may be programmed with multiple activation codes that are provided to each user. For each method  3600 , a new activation code is required and entered to enroll a new user/finger, which is made convenient by the fact that the data input overlay was not removed during enrollment of the previous fingerprint. 
       FIG. 37  is a flowchart illustrating an embodiment of a simple, cost effective method  3700  to enroll a biometric template, such as a fingerprint template, on a device that has limited ability to provide feedback to the user, such as a smart card, without requiring entry of activation data (i.e., an activation code) prior to enrolling the fingerprint template. 
     In step  3702 , a fingerprint-enabled smart card is manufactured. A data input device, such as the overlay described in  FIGS. 34A-34E , may be temporarily connected to the smart card. The card provider may optionally set the status of the smart card as inactive to prevent unauthorized use before the intended user can enroll a fingerprint template and contact the card provider to activate the card. 
     In step  3704 , the card provider provides the smart card and the data input device with integral power source to the user. For example, the card provider may provide the smart card and the data input device with integral power source to the user by mail, courier or directly at a bank or a retail outlet. The card and data input device may be packaged such that the power circuit cannot be completed accidentally during transit. 
     In step  3706 , the user connects the smart card to the power source by completing the power circuit. For example, the power circuit may be completed by folding the data input device such that conductive contact pads align or by removing a pull tab separating the power source from the smart card. Accordingly, connecting the smart card to the power source does nothing but provide power to the electrical components of the smart card—e.g., LED, logic elements, sensor elements, etc.—and the power source is unable to transmit data to or from the smart card. 
     In step  3708  one or more trigger events are detected that results in the fingerprint sensor being put into enrollment mode. An example trigger event may be based on the non-expiration of a timer or a counter. For example, the trigger event may be detecting that the timer or counter has not expired. In such embodiments, a user can enroll a biometric template within a certain time after the fingerprint sensor is put into enrollment mode. In other embodiments, the trigger event may be detecting that the age of the smart card is under a certain age limit which is tracked, for example, by the timer or the counter. The counter may be incremented each time a biometric template has been successfully enrolled or whenever the smart card was used. In such embodiments, the trigger event may be detecting that the counter has not exceeded a predetermined threshold (e.g., a predetermined number of biometric template enrollments or card uses). 
     Another example trigger event may include an occurrence of an error state. A software or hardware component error may occur during the enrollment. An error recovery procedure initiated in response to such software or hardware component error may be the trigger event. In such embodiments, the software or hardware component error would have to be a recoverable error (e.g., a minor error, a transient event or a glitch). Thus, detection of a recoverable error that precluded completion of the enrollment process would cause the sensor to enter enrollment mode. In such embodiments, a non-recoverable error occurring during the enrollment (e.g., a component on the card fails) would not initiate or constitute a trigger event. 
     Other example trigger events include detection of a flag set last time the card was inserted in a card reader (for example a flag set when the card is inserted into a card reader that transmits data to or from the card and instructing the card to enter enrollment mode the next time the card is connected to power), detection of a lack of an enrolled fingerprint template on the card, or detection that power has been provided to the card. Some further trigger event examples may include detection that the card has been inserted into a power source that has connection to only power contacts on the card and no data transmission contacts. In some embodiments, other events or a combination of such events may comprise trigger events. The trigger event may be detected by the fingerprint sensor, by another component on the card (e.g., the secure element module) or the trigger event may be detected as a result of the fingerprint sensor and another component on the card interacting, e.g., a handshake. In some embodiments, if a component other than the fingerprint sensor detects the trigger event, the component may signal the fingerprint sensor to enter enrollment mode. 
     The enrollment mode may be triggered, but the user may not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     The card remains in enrollment mode until disconnected from the power source or until the enrollment is complete. If the card is disconnected from the power source before enrollment is complete, the process may move back to step  3706 , in which an appropriate trigger event may result in the fingerprint sensor being put back into enrollment mode. In some embodiments, the user may be required to take some action, such as, for example, contact the card provider or obtain a new card. In such embodiments, the user may enable the new card to be put into enrollment mode. 
     In some embodiments, the card receives power from the power source, and a status indicator on the smart card (e.g., an LED) may indicate to the user that the one or more power transmission contacts of the power source are connected to the power source (i.e., the card is powered), that the fingerprint sensor is in enrollment mode, and that the smart card is ready for enrollment to start. 
     In step  3710 , the user can now start to enroll a fingerprint. The fingerprint may be enrolled by storing a fingerprint template derived from one or more fingerprint images generated by placing a finger on the fingerprint sensor. The smart card must remain connected to the power source throughout the enrollment process. In some embodiments, however, the smart card may be disconnected from the power source during the enrollment process. In such embodiments, the enrollment mode in the fingerprint sensor is automatically deactivated. In some embodiments, reconnecting the smart card to the power source moves the process back to step  3706 , in which an appropriate trigger event will result in the fingerprint sensor being put back into enrollment mode. The enrollment process is complete when a sufficient fingerprint template is acquired and stored in the fingerprint sensor (e.g., as described in previously incorporated U.S. Pat. No. 9,684,813). Once the enrollment process is complete, enrollment mode in the fingerprint sensor is disabled permanently. In some embodiments, once the enrollment process is complete, enrollment mode in the fingerprint sensor is disabled until a fresh trigger event occurs. The status indicator may provide an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for the fingerprint template and confirm that the enrolling step is successfully complete, e.g., by the LED illuminating for longer period, such as 10 or more seconds. In other embodiments, more than one LED may flash different colors to communicate the various indications described herein. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     In step  3712 , the user removes the data input device from the smart card, and the data input device may be discarded. The user may remove the data input device after successful enrollment, possibly after additional data input. 
     The card provider may set the status of the card as inactive at step  3702 . In such embodiments, the user must activate the card before attempting to use it in step  3714 , in which the user contacts the card provider (e.g., by phone, app, internet, etc.) to activate the smart card. In some embodiments, the user must provide acceptable user verification details to the card provider in order to activate the smart card. If the user is verified, the card provider sets the card status as active in their systems. The user is now able to use the card in the normal way to pay for items, but now requiring fingerprint verification in order to use the smart card. If the user is not verified, the card remains inactive and cannot be used. 
     A device including an overlay providing only a power source, such as the overlay  3402 F described in  FIG. 34F  and the overlay  3502  described in  FIG. 35  may be enrolled by other methods not requiring data input by the user, such as method  2300  shown in  FIG. 23A  or method  2314  shown in  FIG. 23B . 
     In an example of an overlay described herein, the overlay provides power to the smart card to which the overlay is applied, data or signals indicative of the enrollment status of the smart card biometric sensor are provided to the overlay by the smart card or are detected in the smart card by detection circuitry in the overlay, no data is transmitted from the overlay to an external device, and status indicators—such as LED lights—on the overlay (and, optionally, on the smart card as well) are activated to indicate the enrollment status. The enrollment status indicated may include one or more of the following: the smart card biometric sensor is (or is not) in an enrollment mode, the user should provide a biometric image (e.g., place a finger on the a fingerprint sensor), a biometric image provided by the user is (or is not) accepted, the biometric enrollment template is (or is not) complete, the enrollment mode is terminated. The overlay may only provide power to the smart card, or the overlay may also include one or more data input keys for inputting data from the overlay to the smart card. The overlay may optionally include a finger guide as described herein attached to the overlay and may optionally include status indicators associated with finger guide channels as described herein for guiding or instructing a user with respect to placement of a finger on a finger guide channel. The overlay may optionally include status indicators adjacent to a fingerprint sensor of a smart card to which the overlay is applied for guiding or instructing a user with respect to placement of a finger on the sensor, and the finger guide channels may be omitted. 
     In another example of an overlay described herein, the overlay provides power to the smart card to which the overlay is applied, no data or signals are provided to the overlay by the smart card, no data is transmitted from the overlay to an external device, and status indicators—such as LED lights—on the smart card are activated to indicate the enrollment status of the smart card biometric sensor. The enrollment status indicated may include one or more of the following: the smart card biometric sensor is (or is not) in an enrollment mode, the user should provide a biometric image (e.g., place a finger on the a fingerprint sensor), a biometric image provided by the user is (or is not) accepted, the biometric enrollment template is (or is not) complete, the enrollment mode is terminated. The overlay may only provide power to the smart card, or the overlay may also include one or more data input keys for inputting data from the overlay to the smart card. The overlay may optionally include a finger guide as described herein attached to the overlay and may optionally include status indicators associated with finger guide channels as described herein for guiding or instructing a user with respect to placement of a finger on a finger guide channel. The overlay may optionally include status indicators adjacent to a fingerprint sensor of a smart card to which the overlay is applied for guiding or instructing a user with respect to placement of a finger on the sensor, and the finger guide channels may be omitted. 
     As stated above, it is preferable that the fingerprint template is of sufficient quality, otherwise the user may experience a high rate of false rejections or false acceptances. This can be a particular problem when the user is unfamiliar with the goal of the enrollment stage, which is to capture multiple broad, good quality images of as much of the pad of the finger as possible. If the user does not know that the user needs to get images taken of all of the user&#39;s finger pad, including the sides and the tip as well as the central portion of the pad, the user may be inclined to repeatedly present the same portion of their finger during enrollment, thus restricting the coverage of the fingerprint template and increasing the chances of getting a false rejection. 
     It has been observed that the pressure and angle that a user presents their fingerprint during enrollment is different to how they present their finger in daily use of their device. For example, one might enroll a thumb on a smart card by repeatedly touching the fingerprint sensor when the smart card is lying flat. This is likely to result in a fingerprint template of the central pad of the thumb being captured. However, when the smart card is actually being used, the user is likely to either hold the card in a pincer grip to either insert it into the base of a Point of Sale (PoS) device in the case of a contact smart card, or to hold the card over the PoS until the transaction is registered in the case of a contactless smart card. In such contact and contactless use cases, the tip of the thumb print is typically contacting the sensor when the smart card is in use. That is, a part of the thumb, for example the tip of the thumb, is likely to have been missed from the fingerprint template during an enrollment carried out on a card which was lying flat throughout the enrollment process. 
     The problems above concern difficulties that occur during the enrollment process on a limited device. A further complication for a input/feedback-limited device is that once the enrollment process is complete, if the user begins to use their device and then finds their fingerprint is not being recognized reliably, the user may not have a mechanism by which they can re-enroll their finger to create a better fingerprint template and thereby improve their user experience. Re-enrollment on a limited device may be deliberately prohibited for security reasons, for example, the device manufacturer may not want to create a “back door” by allowing the fingerprint template to be changed by an unauthorized user, or it may simply not be practical for the user to interact with the device in order to put it back into an “enroll” mode and hence re-enroll their finger. In such situations, it becomes critical to the user experience that their finger is enrolled properly the first time because there are no second chances to change the fingerprint template. A smart card is a good example of an input/feedback-limited device where a user would be unlikely to get the opportunity to re-enroll their finger should the first fingerprint template not be adequate. 
     In some devices, such as laptop computers or door entry systems, fingerprint sensors may be surrounded by shaped finger guides, such as a beveled peripheral edges, to force the user to place their finger on the sensor in an optimal way. These guides are permanent features of the device. That is, the guides are present when the user enrolls their finger and remain in place when the user is actively using their device. Such guides are designed firstly to ensure that the most useful part of the finger is enrolled for user verification (i.e., the center of the finger pad) and secondly, to increase the chances that the same part of the finger that was initially enrolled will be placed on the sensor during everyday use. An example is described in European Patent Application No. EP 1812890, entitled “Finger Guide Device,” the disclose of which is incorporated by reference in its entirety. For many devices however, it is impractical to change the form factor in order to have permanent finger guides in place, or it is undesirable in relation to design aesthetics to have such permanent finger guides. For example, it would be unacceptable for a smart card to have a permanent finger guide in place since the card would no longer fit in standard ATM machines, purses or wallets. 
     Another existing solution to the above noted problem is to guide the user to present different parts of their finger during enrollment using a graphic on a user interface on the device. Such a solution is described in U.S. Pat. No. 9,715,616, entitled “Fingerprint Sensing and Enrollment,” the disclosure of which is incorporated by reference in its entirety. In some embodiments, the graphic on the user interface shows a representation of a fingerprint which gets gradually shaded in as images of the left, right, top, bottom, etc. of the fingerprint are captured, thus encouraging the user to present different parts of their finger during the enrollment process. This solution, however, is limiting in the sense that it is difficult to convey to the user how a captured image of a fingerprint relates to any particular part of their finger when the device that contains a fingerprint sensor has no, or a limited, user interface. 
     Another existing solution is to employ dynamic enrollment. More specifically, a method in which a fingerprint template is gathered and adapted over time to take account of changes of the way a finger is presented in daily use. That is, the fingerprint template may actively evolve because new captured images are added to it through daily use. An example of a dynamic enrollment method is presented in U.S. Patent Application Publication No. US2014/0003681, entitled “Zero Enrollment,” the disclosure of which is incorporated by reference in its entirety. However, dynamic enrollment may be prohibited for certain devices containing fingerprint sensors due to security concerns that an unauthorized user could successfully enroll their finger by repeatedly presenting their finger such that the fingerprint template evolves to the point where their finger will be accepted. 
     As explained herein, another existing solution for enrolling a fingerprint on a input/feedback-limited device requires the user to visit a secure location, such as a bank, at which the user will perform the enrollment procedure. Such a solution, however, includes various disadvantages particularly related to the inconvenience to the user and possible security breaches as already discussed herein. 
     Rather than have a user attend a secure location, alternative solutions have been proposed to enroll a finger on an input/feedback-limited device containing a fingerprint sensor. However, such alternative solutions require the device containing the fingerprint sensor to be connected to a second connected device, for example, a smartphone or computer terminal, such that instructions and feedback may be given to the user during enrollment via a user interface of the second connected device. This method is far from ideal because not only does it require the user to have ready access to a second device, but also because it requires the device manufacturer and the fingerprint sensor manufacturer to be able to communicate through a myriad of secondary devices. This method also presents significant security concerns because the user is enrolling their fingerprint on a device which is actively connected to a second connected device which may be connected to other networks. 
     The embodiments described herein provide systems, devices and methods of enrolling a fingerprint on a device with limited to no user interfaces or status indicators which can be carried out by the user in their own home, without the need to visit a secure location to carry out enrollment and without requiring the user to connect their card to another connected device such as a smart phone. Complementary systems, devices and methods to those described herein improve the quality and coverage of the enrolled fingerprint template, thus enhancing the security and improving the accuracy of fingerprint matching for the limited device. 
     Such complementary systems, devices and methods include a guide for placement of the finger (where the definition of finger includes a thumb) on a fingerprint sensor during enrollment of the finger. The guide is shaped to increase the likelihood that images of many diverse portions of the fingerprint are obtained when enrolling using a fingerprint sensor with a small area compared to the area of the pad of a typical finger or thumb, in particular capturing images from the longitudinal segment of the fingerprint running from fingertip to knuckle that is richest in fingerprint minutiae, leading to a more complete enrolled fingerprint template (or set of fingerprint templates) and therefore more reliable user verification. In some embodiments, the guide is removably attached to the surface of the device in operative proximity to the sensor and is removed after enrollment is complete. The guide is typically not used during regular operation (e.g., user verification) with the fingerprint sensor. 
       FIGS. 38-40  show an example of a removable finger guide. In various embodiments, the guide  3802  comprises a base plate  3804  which conforms to the surface of the host device  104  containing the fingerprint sensor  102 . In  FIGS. 38-40  the host device  104  shown is a flat smart card, hence the base plate  3804  is flat, however, for example, if the surface of the host device was curved (e.g., a control lever in a car), then the base plate  3804  could be shaped appropriately to make a snug fit with the surface of the device  104  surrounding the fingerprint sensor  102 . The finger guide  3802  may be made of any suitable material, such as molded plastic. The base plate  3804  is removably attached to the surface, for example, held in place with repositionable adhesives such as those provided by companies such as 3M, Krylon, Franklin Adhesives and Polymers, and Bostik. In some embodiments, the finger guide  3802  may be slid over the host device  104 , clipped onto the host device  104 , or folded onto the host device  104  rather than adhering to the device  104  surface. If the host device  104  is metal or includes metal components, the finger guide  3802  may be magnetic and thus stick to the device  104  surface. The base plate  3804  may extend over the edges of the host device  104 . As shown in  FIG. 38 , the base plate  3804  comprises a cut out  3810  to reveal the sensing area  106  of the fingerprint sensor  102  when the finger guide  9802  is placed in operative proximity to the fingerprint sensor  102 . 
     The finger guide  3802  further comprises one or more finger guide channels (also referred to herein simply as “channel” or “channels”) used to capture diverse images of the user&#39;s finger pad. In  FIG. 38 , the finger guide  3802  has three channels: channel A  3806 A, channel B  3806 B, and channel C  3806 C. With the finger guide  3802  secured (e.g., temporarily) to the host device  104  in operative proximity to the fingerprint sensor  102 , each of the channels  3806 A-C is configured to position a finger placed thereon in a unique orientation with respect to the fingerprint sensor  102 . The finger guide channels  3806 A-C may be configured with curved walls and have a width corresponding to a typical finger width. 
     In some embodiments, the base plate  3804  has a raised section  3808 , parallel to one side of the sensing area  106 , on which channel C  3806 C is formed as shown in  FIG. 38 . The raised section  3808  is used to tip the user&#39;s finger up to orient the user&#39;s fingertip to touch the sensor rather than the center of the finger pad. The raised section  3808  may be a ramp with the lowest point of the ramp situated at one edge of the fingerprint sensor  102 . The raised section  3808  may be ergonomically shaped to encourage the user to rest their finger in it. A front stop  3812  may be present on the opposite side of the sensor to the raised section  3808  to stop the user&#39;s fingertip from sliding off the sensor. 
       FIG. 39  shows an embodiment of the finger guide  3802 . As shown in  FIG. 39 , the channels  3806 A-C may be indicated by markings  3902  (e.g., arrows or lines) on the base plate  3804 . For example, the base plate  3804  may be marked with indicia, such as lines, curves, arrows, etc., to indicate how far the finger should be inserted into each channel  3806 A-C such that the finger pad touches the fingerprint sensor sensing area and doesn&#39;t extend too far or fall too short. In some embodiments, the channels  3806 A-C may be ergonomically shaped. In some embodiments, the channels  3806 A-C may have side walls to guide the finger into each channel  3806 A-C. 
       FIG. 40  is a top perspective view of the finger guide with directional finger placement arrows superimposed thereon according to some embodiments. In  FIG. 40 , three channels are shown, indicated by channels A  3806 A, B  3806 B, and C  3806 C. Arrows A and B in  FIG. 40  show the direction of a finger approaching the sensing area  106  via channels A  3806 A and B  3806 B, respectively. Arrow C in  FIG. 40  shows the direction of a finger approaching the sensing area  106  via the raised section  3808 , i.e., channel C  3806 C. 
       FIG. 41  shows a top perspective view of a finger guide  4102  according to some embodiments. As shown in  FIG. 41 , the finger guide  4102  is T-shaped while comprising the same essential features as the finger guide  3802  described in  FIGS. 38-40 . For example, the finger guide  4102  comprises a base plate  3804 , channels A  3806 A, B  3806 B, and  3806 C, a front stop  3812 , a raised section  3808 , and a cut-out  3810  to expose the sensing area  106  of the fingerprint sensor. 
     The channels  3806 A-C of the finger guide  3802 ,  4102  may be the width of a human finger. In some embodiments, different sized finger guides  3802 ,  4102  could be made available to suit a range of fingers, e.g., small, medium or large, rather than one size to fit all. The cut out  3810  needs to fit around the sensing area  106  of the fingerprint sensor, typically a square of 8×8 mm, 9×9 mm or 9.5×9.5 mm, however other sensor size or shapes may be catered for. 
     The finger guide  3802 ,  4102  may be decorated with indicia. For example, pictures of fingers, or finger images may be inscribed on the finger guide  3802 ,  4102  surface so that it is clear to a user where to put their fingers. 
     A method of enrollment that makes use of a temporary, inexpensive, “off-grid” power source is described herein. Specific examples include the card holder/power source  920  shown in  FIGS. 9E-9G . In some embodiments, the finger guide  3802 ,  4102  described in  FIGS. 38-41  may be placed over the sensor at the same time as the device is provided with power using the power sources described herein. 
     An alternative implementation of the temporary power source may include an integrated finger guide, such as is shown in  FIGS. 42-45 . In the illustrated embodiment, a power source/finger print guide  4200  includes a card holder frame  4202  defining card guide rails, including a first longitudinal slot  4204 , a second longitudinal slot  4206 , and a lateral slot  4208  into which a smart card  104  (shown in phantom lines in  FIGS. 44, 45 ) may be inserted. A battery  4220  (shown only in  FIGS. 44, 45 ) may be carried in a suitable battery holder mounted to the card holder frame  4202  and connected by appropriate conductive elements to power transmission contacts of the card  104  as described above. The power source may be powered by mains (e.g., via a USB connector) or solar powered. In other embodiments, if the smart card  104  contains an on-board power source, such as a solar cell, an external power source is not required. 
     A finger guide  4201  may be attached to or integrally formed with the card holder frame  4202 . The finger guide  4201  may include a portion of the card holder frame  4202  forming a base plate  4222  of the finger guide (i.e., the portion of the finger guide having a surface that contacts the surface of the card), an A-channel wing  4210 , a B-channel wing  4212 , a C-channel wing (or raised section)  4214 , a front stop  4218 , and a cut out  4216  through which a sensing portion  106  of the inserted card  104  is exposed. In this context the “wing” may comprise a panel disposed on and extending beyond the base plate  4222 . 
     In some embodiments, the power source with integrated finger guide is a simple rectangular sleeve. For example, the connector housing  904  of the power source  902  shown in  FIG. 9A  could be extended to cover more of the card, including the sensor, and a finger guide could be mounted on top of the housing and a cut out provided in the housing to expose the sensor. 
     The finger guide channels  4210 ,  4212 , and  4214  may include indicia—such as letters “A,” “B,” and “C” to uniquely identify each channel, as shown in  FIGS. 43 and 45 . 
     In a similar way, the temporary power source shown in  FIGS. 34A-34C  and described above may be modified to include an integrated finger guide according to some embodiments. For example, a finger guide, such as those shown in  FIGS. 38-41  made from a molded plastic may be secured to the overlay  3402  with the finger guide cutout  3810  aligned with cutout  2620  of the overlay  3402 . 
     A finger guide, such as those shown in  FIGS. 38-41 , may also be incorporated into a data input device having a cutout exposing a part of the fingerprint sensor, such as those shown in  FIGS. 21A-21D, 26A-26C, 28, and 34A-34F . 
     An alternative implementation of an integrated temporary power source and finger guide is shown in  FIGS. 46A-46B . In the illustrated embodiment, a power source/finger print guide  4600  includes a card holder frame  4602  defining card guide rails, including a card housing slot  4604  and a longitudinal slot  4606  into which a smart card  104  (shown in phantom lines in  FIG. 46A ) may be inserted. A panel  4608  may be secured to or an integral top part of the card holder frame  4602 . The panel  4608  may extend over the card holder frame  4602  and may display instructions to the user. A battery  4620  (shown only in  FIG. 46A ) may be carried in a suitable battery holder mounted to the card holder frame  4602  and connected by appropriate conductive elements to power transmission contacts of the card  104  as described above. The power source may be powered by mains (e.g., via a USB connector) or solar powered. In other embodiments, if the smart card contains an on-board power source, such as a solar cell, an external power source is not required. 
     A finger guide  4601  may be attached to or integrally formed with the card holder frame  4602 . The finger guide  4601  may include an A-channel wing  4610 , a B-channel wing  4612 , a C-channel wing (or raised section)  4614  with a beveled front edge  4622 , a front stop  4618  having a curved contour to accommodate the curved tip of a finger placed on the C-channel  4614 , and a cut out  4616  through which a sensing portion  106  of the inserted card  104  is exposed. The finger guide  4601  and card holder frame  4602  could be made of any suitable material, such as molded plastic. 
       FIGS. 47A-47F  show a finger guide  4702 , such as those shown in  FIGS. 38-41 and 48A -B, incorporated into a data input device in the form of an overlay  4704  integrating a power source according to some embodiments. As shown in  FIGS. 47A-47F , the finger guide  4702  is incorporated into the overlay  4704  integrating the power source with a host device (e.g., smart card  104 ) disposed beneath the overlay  4704 . The finger guide  4702  may be incorporated into any overlay or data input device having a cutout exposing a part of the fingerprint sensor, such as those shown in  FIGS. 26A-26C, 28 and 34A-34F . The finger guide  4702  may be incorporated into an overlay without a data input configuration while having a cutout exposing a part of the fingerprint sensor  106 . Such embodiments of the finger guide  4702  incorporated in an overlay  4732  without a data input configuration are described in further detail in  FIGS. 47G-47H . 
     In the embodiment described in relation to  FIGS. 47A-47H , a smart card  104  is the device containing the fingerprint sensor  102 . However, the application of the finger guide  4702  and the overlay  4704 ,  4732  is not restricted to a smart card and can be used for any device that contains a fingerprint sensor in alternative embodiments. In some embodiments, the smart card  104  comprises the fingerprint sensor  102  with a sensing area  106 , possibly LEDs or other status indicators, and contact pads  108  providing contacts for an external power source. 
     In some embodiments, the overlay  4704 ,  4732  comprises a thin material, e.g., a film that conforms to a surface of the host device when secured thereto. The overlay  4704 ,  4732  may comprise an adhesively-backed sticker or film temporarily and removably placed over the card  104 . In some embodiments, repositionable adhesives provided by companies such as 3M, Krylon, Franklin Adhesives and Polymers, and Bostik may be applied to the overlay  4704 ,  4732  to temporarily place over the portion of the card  104  including the contact pads  108 . In other embodiments, the temporary overlay  4704 ,  4732  may be slid over the device, clipped onto the device, or folded onto the device rather than adhering to the device surface. The overlay may be magnetic and stick to the device surface if the device is metal. 
       FIGS. 47A-47B  show top perspective views of the finger guide  4702  incorporated into the data input device in the form of an overlay  4704  integrating a power source with a host device (e.g., smart card  104 ) disposed beneath the overlay  4704 . A cutout  4713  in the overlay  4704  and a cutout  4715  in the finger guide  4702  exposes a portion of the sensing area  106  while another portion of the sensing area  106  remains covered. As described above, the covered portion of the sensing area  106  is referred to as portion X and the exposed portion of the sensing area  106  is referred to as portion Y. In some embodiments, the overlay  4704  comprises data input keys  4706 A-F on a top surface of the overlay  4704 . In such embodiments, the overlay  4704  comprises corresponding connection traces  4708 A-F on a bottom surface of the overlay  4704 . The connection traces  4708 A-F electrically couple each data input key with an associated spatially distinct portion of the sensing area  106 . In some embodiments, each of the associated spatially distinct portions is within portion X of the sensing area  106  covered by the overlay  4704 . 
     A portion of the overlay  4704  covers the contact pad  108  of the device  104 . The overlay  4704  comprises power connection traces  4722 A (shown only in  FIGS. 47D-47F ),  4722 B (shown only in  FIGS. 47D and 47F ) and card contacts (not shown in  FIGS. 47A-47F ) that contact power pads (e.g., power terminals) of the contact pad  108  when the overlay  4704  is applied to the card  104 . In some embodiments, the card contacts include a contact power input and a ground connection. The overlay  4704  may comprise a suitable power element  4726  (shown only in  FIGS. 47D-F ) to power the card  104  and sensor  102 , such as a small cell battery LR44. In such embodiments, the power element  4726  is securely attached to the overlay  4704  and makes electrical contact with a power element contact pad  4730  (shown in phantom lines in  FIG. 47F ) of the overlay  4704 . For example, one terminal of a battery may contact the power element contact pad  4730 . A power connection trace  4722 B connects the ground connection to the power element contact pad  4730  and a power connection trace  4722 A connects the contact power input to a conductive contact  4724  (shown only in  FIGS. 47D-47F ). In some embodiments, the power connection traces  4722 A,  4722 B, the card contacts (e.g., the contact power input and the ground connection), the power element contact pad  4730 , and the conductive contact  4724  are etched or printed in metal, metalized paint, conductive ink, conductive polymer, or any conductive coating on the bottom side of the overlay  4704 . Any appropriate routing arrangement for the power connection traces  4722 A,  4722 B on the bottom surface of the  4704  overlay is possible with the requirement that the routing of the power connection traces  4722 A,  4722 B must avoid the exposed portion of the sensing area  106  and the connection traces  4708 A-F for the data input keys  4706 A-F. 
     The finger guide  4702  may be attached to or integrally formed with the overlay  4704 . In the illustrated embodiment, finger guide  4702  includes three finger guide channels: an A-channel wing  4712 , a C-channel wing  4714 , a B-channel wing (or raised section)  4716  with a beveled front edge  4718 , a front stop  4720  positioned to be engaged ty the tip of a finger placed on the B-channel  4716 , and the cut out  4715  through which a sensing portion  106  of the inserted card  104  is exposed. The finger guide  4702  could be made of any suitable material, such as molded plastic. 
     In various embodiments, finger guide  4702  further comprises a lever  4710  configured to enable a user to selectively close a power circuit between the power element  4726  and the terminals of the electronic device to enable power transmission between the power element  4726  and the electronic device. The lever  4710  and the circuit closure will be described in further detail in  FIGS. 47C-47F . 
       FIG. 47C  shows a top view of the finger guide  4702  incorporated into the overlay  4704  with a magnified view of the lever  4710 . In some embodiments, the lever  4710  is a single use switch that the user may push down in order to close the power circuit, i.e., power on the fingerprint sensor. In such embodiments, the finger guide  4704  may comprise a latch or detent configured to catch the lever  4710  when pushed down by the user and keep the lever  4710  in the pushed down position. The lever  4710  may be an on-off rocker switch or a dome, plunger, or blister switch. 
       FIGS. 47D-47F  show various bottom views of the finger guide  4702  incorporated into the data input device in the form of an overlay  4704  integrating a power source with a host device (e.g., smart card  104 ) disposed beneath the overlay  4704 . As shown in  FIGS. 47D-47F , the power element  4726  is attached on the bottom surface of the overlay  4704  over the power element contact pad  4730  (shown only in  FIG. 47F ). In some embodiments, the power element  4726  is attached to the bottom surface of the overlay  4704  underneath the finger guide  4702 . In such embodiments, the finger guide  4702  provides a stiffening effect for the overlay  4704  and further support for the power element  4726 . 
     The conductive contact  4724  is positioned underneath the lever  4710  (not shown in  FIGS. 47D-F ). In some embodiments, a portion of the overlay  4704  is cut out such that the overlay  4704  is surrounding the conductive contact  4724 . A conductive spring clip may contact one terminal of the power element  4726 . Accordingly, when the user pushes the lever  4710  down, the conductive contact  4724  is also pushed down and makes contact with the conductive spring clip  4728  extending from the power element  4726 , thereby closing the power circuit between the power element  4726  and the power transmission contacts or terminals of the electronic device (e.g., smart card  104 ) to enable power transmission between the power element  4726  and the electronic device. Once the user has completed an enrollment process using the fingerprint sensor  102 , the configuration of the finger guide  4702  incorporated into the overlay  4704  makes it convenient for the user to grip a portion of the finger guide  4702  extending out of the smart card  104  and peel the finger guide  4702  and the overlay  4704  off of the smart card  104 . Peeling the finger guide  4702  and the overlay  4704  off of the smart card  104  disconnects the power transmission between the power element  4726  and the smart card  104 . 
       FIGS. 47G-47H  show various top views of an embodiment of the finger guide  4702  incorporated into the overlay  4732  comprising a power source. In the illustrated embodiment shown in  FIGS. 47G-47H , the overlay  4732  does not comprise a data input device. Accordingly, the overlay  4732  does not include the data input keys and corresponding conductive traces as described above in  FIGS. 47A-47F . As such, the size of the overlay  4732  may be minimized to save cost of manufacture. 
     As described above, a portion of the overlay  4732  covers the contact pad  108  of the device  104 . The overlay  4704  comprises power connection traces  4722 A,  4722 B and card contacts that contact power pads (e.g., power terminals) of the contact pad  108  when the overlay  4732  is applied to the card  104 . In some embodiments, the card contacts include a contact power input  4734  and a ground connection  4736 . The overlay  4732  may comprise a suitable power element, as described above in  FIGS. 47A-47F , to power the card  104  and sensor  102 , such as a small cell battery LR44. In such embodiments, the power element is securely attached to a bottom surface of the overlay  4732  and makes electrical contact with a power element contact pad of the overlay  4732 . For example, one terminal of a battery may contact the power element contact pad. A power connection trace  4722 B connects the ground connection to the power element contact pad and a power connection trace  4722 A connects the contact power input to a conductive contact. In some embodiments, the power connection traces  4722 A,  4722 B, the card contacts (e.g., the contact power input  4734  and the ground connection  4736 ), the power element contact pad, and the conductive contact are etched or printed in metal, metalized paint, conductive ink, conductive polymer, or any conductive coating on the bottom side of the overlay  4732 . 
     The finger guide  4702  may be attached to or integrally formed with the overlay  4732 . As described above in  FIGS. 47A-47F , the finger guide  4702  comprises the lever  4710  configured to enable a user to selectively close a power circuit between the power element and the terminals of the electronic device (e.g., the smart card  104 ) to enable power transmission between the power element and the electronic device. Once the user has completed an enrollment process using the fingerprint sensor  102 , the configuration of the finger guide  4702  incorporated into the overlay  4732  makes it convenient for the user to grip a portion of the finger guide  4732  extending out of the smart card  104  and peel the finger guide  4702  and the overlay  4732  off of the smart card  104 . Peeling the finger guide  4702  and the overlay  4732  off of the smart card  104  disconnects the power transmission between the power element and the smart card  104 . 
       FIGS. 47I-47L  illustrate an embodiment of an overlay including a finger guide  4702  comprising a switch  4738 . In the illustrated embodiment shown in  FIGS. 47I-47L , the finger guide  4702  comprising the switch  4738  is incorporated into an overlay  4748  comprising a power element  4726 , where the overlay  4748  does not comprise a data input device as described above in  FIGS. 47G-47H . In other embodiments, the finger guide  4702  comprising the switch  4738  may be combined with a data input device in the form of an overlay integrating a power element as described above in  FIGS. 47A-47F . 
       FIGS. 47I-47J  show various top views of an embodiment of the finger guide  4702  comprising the switch  4738  configured to enable a user to selectively open and close a power circuit between the power element  4726  (shown in  FIGS. 47J-47K ) and the terminals of the electronic device (e.g., the smart card  104 ) to enable and disable power transmission between the power element and the electronic device. As shown in  FIG. 47I , the switch  4738  may be configured to be movable in direction “A” to close the power circuit, thereby initiating power transmission between the power element and the electronic device according to some embodiments. The switch  4738  may also be configured to be movable in direction “B” to open the power circuit, thereby terminating power transmission between the power element and the electronic device. The initiating and terminating of power transmission between the power element and the electronic device will be described in further detail below in  FIGS. 47K-47L . 
     In some embodiments, the switch  4738  comprises a top surface  4744 , two side walls  4740 A-B (one side wall  4740 A shown in  FIGS. 47I-47J  and the other side wall  4740 B shown in  FIGS. 47K-47L ), and a back wall  4746 . In such embodiments, the finger guide  4702  comprises two slot cutouts  4742 A-B, in which the two side walls  4740 A-B of the switch  4738  are located in, respectively. Accordingly, the slot cutouts  4742 A-B allow a user to move the switch  4738  back and forth in directions A and B, as shown in  FIG. 47I . In some embodiments, the top surface  4744  comprises a raised section (e.g., a handle)  4750  configured to help a user slide the switch back and forth in directions A and B. 
       FIG. 47K  shows a bottom perspective view of an embodiment of the finger guide  4702  comprising the switch  4738 . For the purpose of explanation,  FIG. 47K  shows the switch  4738  with a side wall  4740 A removed. As described above, the power element  4726  is attached on the bottom surface of the overlay  4748  underneath the finger guide  4702 . As shown in  FIG. 47K , a conductive spring clip  4728  comprising a rounded conductive head  4752  at a distal end extends from the power element  4726 . The overlay  4748  comprises a conductive contact  4724  positioned above the head  4752 . The switch  4738  further comprises a bottom base  4746  comprising a stepped surface. In some embodiments, the stepped surface comprises two steps  4754 A-B, each including a curved and smooth top surface. In such embodiments, each surface of the steps  4754 A-B is configured to receive the rounded head  4752 . As shown in  FIG. 47K , the step  4754 A closer to the power element  4726  is lower than the other step  4754 B. Accordingly, when the switch  4738  is pushed back in direction B, the lower step  4754 A receives the head  4752 . The lower step  4754 A is configured to receive the head  4752  such that the head  4752  does not contact the conductive contact  4724 , thereby opening the power circuit between the power element  4726  and the terminals of the electronic device (e.g., the smart card  104 ) to terminate or disable power transmission between the power element and the electronic device. 
       FIG. 47L  shows a side cross sectional view of an embodiment of the finger guide  4702  comprising the switch  4738  along the line L-L in  FIG. 47I . As shown in  FIG. 47L , the switch  4738  is slidable in direction B according to some embodiments. In such embodiments, the lower step  4754 A moves towards the direction of the power element and the higher step  4754 B moves into the previous position of lower step  4754 A. Accordingly, the rounded conductive head  4752  is pushed up into and received by the curved top surface of the higher step  4754 B, as shown by the arrow in dotted line in  FIG. 47L . The higher step  4754 B is configured to receive the head  4752  such that the head  4752  contacts the conductive contact  4724 , thereby closing the power circuit between the power element  4726  and the terminals of the electronic device (e.g., the smart card  104 ) to initiate or enable power transmission between the power element  4726  and the electronic device. 
     The user may move the switch  4738  in direction B to disable transmission between the power element  4726  and the electronic device (e.g., the smart card  104 ). In such embodiments, the step closer to the power element  4726  may be higher than the other step of the bottom base  4746 . Accordingly, moving the switch  4738  in direction A would enable transmission between the power element  4726  and the electronic device. 
     The rounded conductive head  4752  may be separate from the conductive spring clip  4728  and attached to the conductive contact  4724 . In such embodiments, the distal end of the conductive spring clip  4728  may be pushed up and down by the movement of the switch  4738 , as described above, to initiate and terminate transmission between the power element  4726  and the electronic device (e.g., the smart card  104 ). 
     As shown in  FIGS. 47I-47L , the switch  4738  enables a user to selectively initiate and terminate the power transmission between the power element  4726  and the terminals of the electronic device (e.g., the smart card  104 ). The minimal number of components of the switch  4738 , as described above, allows reduction in cost of manufacture. 
     In alternative embodiments to the overlay  4702  shown in  FIGS. 47A-47L  and having a lever  4710  or switch  4738 , the overlay lacks a finger guide. 
       FIGS. 48A and 48B  are right and left partial perspective views of an alternative configuration of a finger guide  4800 . The finger guide  4800  comprises a first channel  4802  (channel A) a second channel  4804  (channel B), and a third channel  4806  (channel C). Note that the channels A, B, and C are labeled differently than in the embodiment described above as the particular labeling, if any, is not critical. The finger guide  4800  further comprises a cut out  4850  for the fingerprint sensor and a front stop (or finger stop)  4808  located across the cut out  4850  from the channel  4804 . 
     In some embodiments, channel  4802  provides a generally flat approach (i.e., parallel to the sensor surface) for a finger placed thereon. In some embodiments, channel  4804  may be raised above the plane of the sensor surface exposed at the cut out  4850  and has a flat upper portion and a steep ramp  4854  (e.g., about 45 degrees) extending to the cut out  4850 . In some embodiments, channel  4806  has a gentle slope (e.g., about 10-15 degrees) extending down to the cut out  4850 . 
     The flat approach of first channel  4802 , the gentle ramp of channel  4806 , and the steep ramps of channel  4804  could be on any side of the sensor (i.e., cut out  4850 ), in any order, but the arrangement shown is ideal for a fingerprint sensor positioned above a long central axis and close to the right-hand short edge of a smart card, such as is illustrated in  FIG. 1 . For example, in a typical bank card, the sensor may be placed in this position so as not to interfere with the secure element module which is typically close to the left-hand short edge of a smart card, or with the printed or embossed symbols and/or a magnetic strip on the smart card, both of which run parallel to, but are positioned below, the long central axis of the card. 
     When holding the card, it is more natural to provide a tip touch at the second channel  4804  because channel  4804  is closest to the short edge of the card, as shown in  FIG. 49A   
     At channel  4806 , the user has to reach over more card material compared to channel  4802 . The gentle slope of channel  4806  is complementary to the resulting thumb position, meaning a different part of the finger surface is more likely to be imaged compared to channel  4802 , as shown in  FIG. 49B . 
     At channel  4802 , the user grasps the card from the long side closest to the sensor, as shown in  FIG. 49C . 
     In some embodiments, the finger guides, and, if applicable, card holder frames, of  FIGS. 38-48  are made of inexpensive materials that can be safely disposed of, for example, plastic, cardboard, rubber, or foam. The materials may be lightweight such that the finger guide may be sent to the user by mail or courier at low cost. The base plate, raised section(s), and channel(s) of the finger guide may be molded in a single unit, or may be separate parts. 
     Finger guides such as those shown in  FIGS. 39-48  require the user to place a finger on the sensing surface at positions that are separated from each other by angles in a plane parallel to the sensing surface and at positions that are elevated with respect to the sensing surface. Thus, such guides provide three-dimensional variation of the finger positions during enrollment. Benefits of such three-dimensional variation are shown conceptually in  FIGS. 50, 51, and 52 . 
       FIG. 50  shows “novice” enrollment (i.e., with no guidance on how to enroll) according to some embodiments. Without guidance, the user typically puts their finger  5006  up and down again in the same or similar places along the finger longitudinal axis  5002 . The user does not rotate their finger with respect to the sensor, and hence the captured images  5004  are not very different from one another. In addition, none of fingertip is captured. This has a particularly adverse impact on user verification results if the device containing the fingerprint sensor is a smart card. Since smart cards are thin and light, they are most likely held between pinched thumb and finger with the thumb tip on the sensor, hence it is important to enroll the tip in the fingerprint template. 
       FIG. 51  shows a two-dimensional “angle” enrollment according to some embodiments. In the “angle” enrollment, the user is encouraged to rotate their finger  5006  relative to the finger longitudinal axis  5002 . For example, the user may rotate their finger  5006  by +/−45 degrees as well as 0 degrees relative to the finger longitudinal axis  5002 . Accordingly, more of the sides of the finger pad may be captured as images  5004  for the fingerprint template, but little more of the longitudinal segment of the fingerprint is captured as the user is likely not going to rotate their finger  5006  much. Since the enrollment showed in  FIG. 51  is two-dimensional, i.e., “flat,” it is unlikely to capture images of fingertip area. 
       FIG. 52  shows a three-dimensional enrollment according to some embodiments. In the three-dimensional enrollment, the user is encouraged to rotate their finger  5006  relative to the finger longitudinal axis  5002  and to use a channel having a ramp. For example, the user may rotate their finger  5006  by +/−90 degrees as well as 0 degrees and use a channel having a steep ramp and/or a channel having a gentle ramp. For the three-dimensional enrollment, the user has to physically rotate the device containing the sensor in order to insert their finger  5006  in the channel, thereby increasing the chances of extending coverage of the fingerprint template because their finger  5006  will almost certainly be placed in a different place than before (e.g., 180 degrees between A and C channels in  FIGS. 48A and 48B ). Having channels with both steep and gentle ramps means the fingerprint template coverage extends to include the fingertip. Accordingly, the result of such three-dimensional enrollment is a greater portion of the longitudinal segment of the fingerprint captured as images  5004  for the fingerprint template as compared to other enrollment techniques. 
     In some alternate finger guide embodiments, two or more different finger guide channels may not be located in fixed positions with respect to the sensing surface as in the finger guides described herein, but may be moved with respect to the sensing surface to selectively place one of the channels in operative proximity to the sensing surface. 
       FIG. 53A  is a top plan view of an alternative finger guide  5302  whereby two or more cut outs  5304 A-C and associated finger guide channels  5306 A-B are linearly moveable with respect to the sensing surface  106  to selectively align the cut out  5304 A-C with the sensing surface  106  and place the associated finger guide channel  5306 A-B in operative proximity to the sensing surface according to some embodiments. The finger guide  5302  is clipped, adhered, or otherwise temporarily attached to a smart card  104 . The smart card may be inserted into a power sleeve  5308  or other power source, such as, for example power source  902  shown in  FIG. 9A , power source  910  shown in  FIG. 9D , power source  920  shown in  FIG. 9F , or any other suitable power source to which the card  104  may be coupled. The finger guide  5302  and power source  5308  could also be connected together or otherwise manufactured as a single, integral unit. 
     As shown in  FIG. 53A , the finger guide  5302  includes a panel  5310  having two or more cutouts  5304 A-C that is slidably or otherwise movably attached to rails  5312 , or other structures allowing linear translation of the panel  5310 , attached to the card. In the illustrated embodiment, the panel includes three cut outs A  5304 A, B  5304 B, C  5304 C that can be selectively aligned with the sensing surface  106  of the card&#39;s fingerprint sensor by moving the panel  5310  with respect to the rails  5312 , and each cut out  5304 A-C has a different finger guide channel configuration. For example, finger cut out A  5304 A has a flat approach by which a finger placed thereon is generally parallel to the surface of the fingerprint sensor sensing surface  106 . Cut out B  5304 B includes a gentle ramp  5306 A whereby a finger placed there and is oriented at an elevation angle of, for example, 10-15° with respect to the sensing surface  106 . A front stop (not shown in  FIG. 53A ) may be provided adjacent the cut out  5304 B on the opposite side from the ramp  5306 A. Cut out C  5304 C may have a steep ramp  306 B whereby the finger is oriented at an elevation angle of, for example, about 45° with respect to the sensing surface  106 . A front stop (not shown in  FIG. 53A ) may be provided adjacent the cut out  5304 C on the opposite side from the ramp  5306 B. 
     The panel  5310  is movable with respect to the rails  5312 , which may be attached to the card  104  such that any of cutouts A, B, or C  5304 A-C can be aligned with the sensing surface  106 . In the embodiment shown in  FIG. 53A , the sensing area  106  is shown through the cut out C  5304 C, which is aligned with the sensing area  106 . In some embodiments, detents or other similar features may be provided to releasably secure the panel  5310  with respect to the guide rails  5312  to resist, but not prevent, translation of the panel  5310  with respect to the rails  5312  such that the panel  5310  will hold a selected linear position. In an embodiment as shown in  FIG. 53B , the underside of the panel  5310  has spaced pins  5314  while the upper side of the rails  5312  have soft teeth  5316  so that the panel  5310  can be slid until a cut out  5304 A-B lines up with the sensing surface  106 . The panel  5310  stays in the selected position during finger enrollment through the aligned cut out. In some embodiments, the user has to push or pull the panel  5310  sufficiently hard to overcome the resistance of the pins  5314  engaging the teeth  5316  to align a different cut out with the sensing surface  106 . 
     In the illustrated embodiment shown in  FIG. 53A , the panel  5310  is movable with respect to the guide rails  5312  and the card  104  in a direction parallel to the long side of the card  104 . The panel  5310  may be movable with respect to the guide rails  5312  and the card  104  in a direction parallel to the short side of the card  104 . 
       FIG. 54  is a top plan view of an alternative finger guide  5402  whereby two or more cut outs  5402 A-C and associated finger guide channels  5306 A-B are rotatably moveable with respect to the sensing surface  106  to selectively align the cut out with the sensing surface  106  and place the associated finger guide channel  5306 A-B in operative proximity to the sensing surface  106  according to some embodiments. The smart card  104  may be inserted into a power sleeve  5308  or other power source, such as, for example power source  902  shown in  FIG. 9A , power source  910  shown in  FIG. 9D , power source  920  shown in  FIG. 9F , or any other suitable power source to which the card may be coupled. The rotatable finger guide  5402  and power source  5308  could also be connected together or otherwise manufactured as a single, integral unit. 
     In the illustrated embodiment shown in  FIG. 54 , the rotatable finger guide  5402  is in the form of a dial or spinner having three cutouts A  5306 A, B  5306 B, C  5306 C. The spinner can be rotated about its center to selectively position one of the cut outs A  5306 A, B  5306 B, or C  5306 C in alignment with the sensor. In the illustrated embodiment shown in  FIG. 54 , cut out C  5306 C is aligned with the sensing surface  106 . 
       FIGS. 55, 56, and 57  illustrate various components of the rotatable finger guide  5402  shown in  FIG. 54 .  FIG. 55  shows an embodiment of the base  5500  of the rotatable finger guide  5402  that may be removably attached to the smartcard  104  or any other fingerprint sensor enabled device. For example, the base  5500  may be removably attached by clips, adhesive, or the like. The spinner base  5500  has an axle  5502  at its center, a base cut out  5504 , and a spindle  5506  for an arm of a position selector. The base  5500  is secured to the smart card  104  with the base cut out  5504  aligned with the fingerprint sensor. 
       FIG. 56  shows a top portion  5600  of the rotatable finger guide  5402  according to some embodiments. The cut outs A, B, and C  5402 A-C are formed in the top portion  5600 . The top portion  5600  may include a number of position selector posts  5602 A-C. The top portion  5600  may further include a center knob  5604  for rotating the top portion. Alternatively, in lieu of the knob  5604 , the user could rotate the top portion, i.e., the spinner,  5600  by its outer peripheral edge. 
       FIG. 57  is a side view of a position selector  5702  of the rotatable finger guide  5402  according to some embodiments. In some embodiments, the position selector  5702  comprises a flexible arm  5704  projected radially from the spindle  5506  of the base  5500 . 
     The top portion  5600  is mounted on the axle  5502  of the base  5500  so that the top portion  5600  can rotate about the axle  5502  when the user turns the knob  5604  or turns the top portion about its edge. The position selector arm  5704  is positioned so that the arm  5704  contacts the position selector posts  5602 A-C of the top portion  5600  to thereby hold the top portion  5600  in a position aligning one of the cut outs A  5402 A, B  5402 B, C  5402 C with the base cut out  5504  and the sensor. To rotate the top portion  5600  and re-position the guide  5402 , the user applies torque to the top portion  5600  to overcome the resilience of the position selector arm and move the position selective post  5602 A-C past the position selector arm  5704  and rotate the top portion  5600  to align the next cut out  5402 A-C with the base cut out  5504  and the sensor. 
     In the illustrated embodiment shown in  FIG. 56 , the top portion  5600  includes three cut outs A  5402 A, B  5402 B, C  5402 C that can be selectively aligned with the sensing surface  106  of the card&#39;s fingerprint sensor by rotating the top portion  5600 , i.e., the spinner, with respect to the base  5500 , and each cut out has a different finger guide channel  5306 A-B configuration. For example, finger cut out A  5402 A has a flat approach by which a finger placed thereon is generally parallel to the surface of the fingerprint sensor sensing surface. In some embodiments, cut out B  5402 B includes a gentle ramp  5306 A whereby a finger placed thereon is oriented at an elevation angle of, for example, 10-15° with respect to the sensing surface  106 . A front stop may be provided adjacent the cut out on the opposite side from the ramp. Cut out C  5402 C may have a steep ramp  5306 B whereby the finger is oriented at an elevation angle of, for example, about 45° with respect to the sensing surface  106 . A front stop may be provided adjacent the cut out on the opposite side from the ramp. In the illustrated embodiment shown in  FIG. 56 , a front stop  5606  is provided on the opposite side from the steep ramp  5306 B. However, a front stop may also be provided on the opposite side from the gentle ramp  5306 A in some embodiments. 
     In some embodiments, more than three cut outs may be provided in the rotatable finger guide  5402  each with different angles of finger guide channel raised sections (also referred to as ramps) and/or with different finger shaped channel walls. 
       FIG. 58  is a flowchart illustrating an embodiment of a simple, cost effective method  5800  to enroll a biometric template, such as a fingerprint template, on a device that has limited ability to provide feedback to the user, such as a smart card and using a power source (such as the power source described above in  FIG. 9F ) and separate finger guide (such as the finger guide described above in  FIGS. 38-41 ), or alternatively using a power source with integrated finger guide (such as the power source with integrated finger guide described above in  FIGS. 42-47 ). 
     In step  5802 , a fingerprint-enabled smart card is manufactured. The card provider may set the status of the smart card as inactive to prevent unauthorized use before the intended user can enroll a fingerprint template and contact the card provider to activate the card. 
     In step  5804 , the card provider provides the smart card and a low-cost, simple power source and a temporary finger guide to the user, e.g., sent by mail or courier or given out by a bank or retail outlet. The power source could be battery powered, powered by mains (e.g., via a USB connector), or solar powered. The finger guide may be separate to the power source, or integrated in the power source. In another embodiment, if the smart card contains an on-board power source, such as a solar cell, an external power source is not required. 
     In step  5806 , the user positions the finger guide around the sensing area of the fingerprint sensor. The smart card may be sent to the user with the finger guide already positioned around the sensor. The user then connects the smart card to the power source by, for example, inserting the card into a power source housing having contacts for connecting one or more power transmission contacts of the smart card to the power source without connecting any data transmission contacts of the smart card to a device configured to transmit data to or receive data from the card. Accordingly, in such embodiments, connecting the smart card to the power source does nothing but provide power to the electrical components of the smart card—e.g., LED, logic elements, sensor elements, etc.—and the power source is unable to transmit data to or from the smart card. In other embodiments, the finger guide may be used in conjunction with a power source including means for transmitting data to or from the smart card. If the finger guide and the power source are a single integrated device, then positioning the finger guide with respect to the fingerprint sensor and connecting the smart card to the power source comprise one single step of inserting the smart card or otherwise operatively coupling the smart card to the integrated device. 
     The smart card and the power source may be sent to the user with the smart card already inserted in the power source. In such embodiments, a battery connection tab is inserted between the power source and the smart card to keep a power connection disconnected. The user may pull out the battery connection tab to connect the power source to the smart card. 
     In step  5808  one or more trigger events are detected that results in the fingerprint sensor being put into enrollment mode. An example trigger event may be based on the non-expiration of a timer or a counter. For example, the trigger event may be detecting that the timer or counter has not expired. In such embodiments, a user can enroll a biometric template within a certain time after the fingerprint sensor is put into enrollment mode. In other embodiments, the trigger event may be detecting that the age of the smart card is under a certain age limit which is tracked, for example, by the timer or the counter. The counter may be incremented each time a biometric template has been successfully enrolled or whenever the smart card was used. In such embodiments, the trigger event may be detecting that the counter has not exceeded a predetermined threshold (e.g., a predetermined number of biometric template enrollments or card uses). 
     Another example trigger event may include an occurrence of an error state. A software or hardware component error may occur during the enrollment. An error recovery procedure initiated in response to such software or hardware component error may be the trigger event. In such embodiments, the software or hardware component error would have to be a recoverable error (e.g., a minor error, a transient event or a glitch). Thus, detection of a recoverable error that precluded completion of the enrollment process would cause the sensor to enter enrollment mode. In such embodiments, a non-recoverable error occurring during the enrollment (e.g., a component on the card fails) would not initiate or constitute a trigger event. 
     Other example trigger events include detection of a flag set the last time the card was inserted in a card reader (for example a flag set when the card is inserted into a card reader that transmits data to or from the card and instructing the card to enter enrollment mode the next time the card is connected to power), lack of an enrolled fingerprint template on the card is detected, detecting that power has been provided to the card, or entry of a PIN code (e.g., via a data entry template coupled to the power source as described above). Still another trigger event may be detection that the card has been inserted into a power source that has connection to only power contacts on the card and no data transmission contacts. Other events, or combinations of events, may be trigger events. The trigger event may be detected by the fingerprint sensor, or by another component on the card (e.g., the secure element module) or may be detected as a result of the fingerprint sensor and another component on the card interacting, e.g., a handshake. If a component other than the fingerprint sensor detects the trigger event, that component may signal to the fingerprint sensor to enter enrollment mode. 
     The enrollment mode may be triggered, but the user may not complete the enrollment. That is, the fingerprint sensor may be in enrollment mode, but the user does not provide any input to the fingerprint sensor for the purpose of gathering sufficient acceptable images for a fingerprint template. In such embodiments, the fingerprint sensor may enter a power saving sleep mode, also referred to as a “wait on finger mode,” to avoid draining the power source. For example, once the fingerprint sensor enters the enrollment mode and does not receive any input from the user for a predetermined period of time, the fingerprint sensor enters the power saving sleep mode and waits for a user touch to wake up and resume the enrollment process. In some embodiments, any acceptable images captured before the fingerprint sensor entered the power saving sleep mode are saved so that the enrollment process continues where the user had left off. In some embodiments, smart card components, such as the secure element module, may enter a sleep mode when the fingerprint sensor enters the power saving sleep mode. Similarly, the smart card components may wake up when the fingerprint sensor wakes up from the power saving sleep mode and resumes the enrollment process. 
     The card remains in enrollment mode until disconnected from the power source or until the enrollment is complete. If the card is disconnected from the power source before enrollment is complete, the process may move back to step  5808 , whereby an appropriate trigger event will result in the sensor being put back into enrollment mode, or alternatively the user may be required to take some action, such as contact the card provider or obtain a new card, to enable the card to be put into enrollment mode. 
     The card receives power from the power source, and a status indicator on the smart card (e.g., an LED) indicates to the user that the one or more power transmission contacts of the power source are connected to the power source (i.e., the card is powered), that the fingerprint sensor is in enrollment mode, and the smart card is ready for enrollment to start. 
     In step  5810 , the user can now start to enroll a fingerprint with the assistance of the finger guide. Step  5810  is described in further detail in  FIG. 59 . The fingerprint is enrolled by storing a fingerprint template derived from one or more fingerprint images generated by placing a finger on the fingerprint sensor. The smart card must remain connected to the power source throughout the enrollment process. In the event the smart card is disconnected from the power source during the enrollment process, the enrollment mode in the fingerprint sensor is automatically deactivated. In some embodiments, reconnecting the smart card to the power source moves the process back to step  5808 , whereby an appropriate trigger event will result in the sensor being put back into enrollment mode. The enrollment process is complete when a sufficient fingerprint template is acquired and stored in the fingerprint sensor (e.g., as described in previously incorporated U.S. Pat. No. 9,684,813). Once the enrollment process is complete, enrollment mode in the fingerprint sensor is disabled permanently or alternatively, until a fresh trigger event occurs. In some embodiments, the status indicator provides an indication to the user when an image is acceptable, e.g., by an LED illuminating for a few seconds, and may indicate when an image is not acceptable, e.g., by the LED flashing several times. The status indicator may indicate to the user when sufficient acceptable images have been gathered for the fingerprint template and confirm that the enrolling step is successfully complete, e.g., by the LED illuminating for longer period, such as 10 or more seconds. In some embodiments, more than one LED may flash different colors to communicate the various indications described above. A flexible display such as an OLED panel may be used to provide textual feedback during the enrollment process. 
     In step  5812 , the user removes the smart card from the power source, thereby disconnecting the one or more power transmission contacts of the smart card from the power source, and the power source may be discarded. The user may also now remove the finger guide (if it is not integrated in the power source) and may dispose of it. 
     If the card provider set the status of the card as inactive at step  5802 , then the user must activate the card before attempting to use it. In step  5814 , the user contacts the card provider (e.g., by phone, app, internet, etc.) to activate the smart card. The user must provide acceptable user verification details to the card provider in order to activate the smart card. If the user is verified, the card provider sets the card status as active in their systems. The user is now able to use the card in the normal way to pay for items, but now requiring fingerprint verification in order to use the smart card. If the user is not verified, the card remains inactive and cannot be used. 
     As discussed above, in step  5810  of  FIG. 58 , the user enrolls their finger on the host device with the assistance of the finger guide.  FIG. 59  breaks down step  5810  of  FIG. 58  as a method  5900  to provide more detail as to how the finger guide assists in the enrollment process. 
     As described above, in step  5808 , a trigger event puts the fingerprint sensor into enrollment mode. Once the fingerprint sensor is put into enrollment mode, the process may begin method  5900  with step  5810 A according to some embodiments. In step  5810 A, the user puts their finger in channel A of the finger guide and touches the sensing area of the fingerprint sensor. The sensor captures an image of the finger and optionally signals to the user if the captured image is acceptable via a status indicator. The user repeatedly lifts and touches the sensor with the same finger via channel A until a total of w acceptable images (touches) have been captured, where w may range between 1-5, for example, 2. The user may lift and touch the sensor with the same finger any number of times before the total of w acceptable images (touches) have been captured and move on to step  5810 B or step  5810 C before returning to step  5810 A to complete the total of w acceptable images. 
     In step  5810 B, the user puts the same finger in channel B of the finger guide and touches the sensing area of the fingerprint sensor. The sensor captures an image of the finger and optionally signals to the user if the captured image is acceptable via a status indicator. The user repeatedly lifts and touches the sensor with the same finger via channel B until a total of x acceptable images have been captured, where x may range between 1-5, for example 2. The user may lift and touch the sensor with the same finger any number of times before the total of x acceptable images (touches) have been captured and move on to step  5810 A or step  5810 C before returning to step  5810 B to complete the total of x acceptable images. 
     In step  5810 C, the user puts the same finger in channel C and touches the sensing area of the fingerprint sensor. The sensor captures an image of the finger and optionally signals to the user if the captured image is acceptable via a status indicator. The user repeatedly lifts and touches the sensor with the same finger via channel C until a total of y acceptable images have been captured, where y may range between 1-5, for example, 2. The user may lift and touch the sensor with the same finger any number of times before the total of y acceptable images (touches) have been captured and move on to step  5810 A or step  5810 B before returning to step  5810 C to complete the total of y acceptable images. 
     In step  5810 D, the enrollment is complete and the process continues to step  5812  described earlier. 
     Steps  5810 A-C may be carried out in any order. For example, the method  5900  may begin with any one of steps  5810 A-C. 
     In some embodiments, the total number of acceptable images (touches) that need to be captured for a sufficient fingerprint template may be the sum of x+y+z. In such embodiments, the user may put the same finger in one channel, for example channel A, B, or C, of the finger guide and repeatedly lift and touch the sensor with the same finger via the same channel until the total number of acceptable images, e.g., x+y+z, are captured. For example, if the method  5900  had begun with step  5810 B, the user may repeatedly lift and touch the sensor with the same finger via channel B until the total number of acceptable images are captured. Once the total number of acceptable images is reached in step  5810 B, enrollment is complete and the process continues to step  5812 . 
     The finger guide may comprise one or more status indicators, such as LEDs, and a controlling processor coupled to the one or more status indicators and configured to assist the user during the enrollment process described in method  5900 . The one or more status indicators may provide an indication to the user regarding which channel of the finger guide to put the same finger in. Referring to the finger guide (such as the finger guide described above in  FIGS. 38-41 ), or alternatively the power source with integrated finger guide (such as the power source with integrated finger guide described above in  FIGS. 42-47 ), each of the finger guide&#39;s channels may comprise one or more status indicators. Accordingly, the controlling processor may be configured to indicate to the user through the one or more status indicators on each channel which channel the user should put the same finger in. For example, one or more status indicators on a C-channel wing may indicate to the user to place the same finger in the C-channel. As a further example, after the user places the same finger in the C-channel, one or more status indicators on a B-channel wing may indicate to the user to subsequently place the same finger in the B-channel. In this way, the controlling processor may guide the user through the enrollment process by indicating which channels of the finger guide to place the same finger in. 
     In some embodiments, capacitive strips may be implemented around the edges of each side of the sensing area corresponding to each channel. For example, a capacitive strip may be placed around an edge of the sensing area corresponding to channel A. Similarly, a capacitive strip may be placed around the remaining two edges of the sensing area corresponding to channel B and channel C. In such embodiments, the fingerprint sensor may be configured to recognize that the user has placed a finger in a certain channel when the finger contacts, or comes within a close proximity to, the corresponding capacitive strip. For example, the fingerprint sensor may recognize that the user has placed a finger in the C-channel when the finger contacts, or comes within a close proximity to, the capacitive strip placed around the edge of the sensing area corresponding to channel C. 
     In an alternative embodiment, such capacitive strips may be implemented in each side of the finger guide&#39;s cutout corresponding to each channel. For example, a capacitive strip may be located on a bottom surface of a side of the cutout corresponding to channel A. Similarly, a capacitive strip may be located on a bottom surface of the remaining two sides of the cutout corresponding to channel B and channel C. In such embodiments, each capacitive strip may slightly overlap with a corresponding edge of the sensing area when finger guide is placed over the fingerprint sensor such that the cutout exposes the sensing area. Accordingly, the fingerprint sensor may be configured to recognize that the user has placed a finger in a certain channel when the finger contacts, or comes within a close proximity to, the corresponding capacitive strip. For example, the fingerprint sensor may recognize that the user has placed a finger in the C-channel when the finger contacts, or comes within a close proximity to, to the capacitive strip located on the bottom surface of a side of the cutout corresponding to channel C. 
     In some embodiments, the finger guide may have only a single channel. Accordingly, the method  5900  of  FIG. 59  may include just step  5810 A. In such embodiments, the process continues to step  5812  after step  5810 A. 
     The finger guide may have only two channels. Accordingly, the method  5900  of  FIG. 59  may include just two step, e.g., step  5810 A and step  5810 B. In such embodiments, the process continues to step  5812  after step  5810 B. 
     The finger guide may be removed after step  5810 C and the user may then touch the sensing area of the fingerprint sensor with the same finger with no guide present. In such embodiments, the method  5900  may include an additional step, in which the sensor captures an image of the finger and optionally signals to the user if the captured image is acceptable via a status indicator. The user repeatedly lifts and touches the sensor with the same finger until a total of z acceptable images have been captured, where z may range between 1-5, for example 2. The process then continues to step  4812 . 
     The process described in the method  5900  of  FIG. 59  is easily extended if the finger guide has more than three channels. 
     The sensitivity of a fingerprint sensor&#39;s performance to a poor enrollment is governed to some extent by the way that the biometric matching algorithm, running in conjunction with that particular sensor hardware, is designed to operate. For example, some biometric algorithms perform matching by minutiae matching, while others employ ridge flow analysis. Fingerprint templates may be created in different ways, such as stitching, or image filtering and sorting. Some biometric algorithms are agnostic to the rotation of the finger with relation to the orientation of the sensor while others are not. It is beneficial if fingerprint sensor device manufacturer understands how fingerprint templates are generated and how its matching algorithms operate. This information, taken with knowledge of how the end user holds and operates the device in everyday use, allows the identification of parts of the finger pad, including peripheral portions, that should be enrolled in order to see reliable user verification in all use cases, when a particular sensor design is running a particular biometric algorithm. 
     For some fingerprint sensor and biometric algorithm combinations, one way to maximize coverage of the minutiae-rich longitudinal segment is to use a finger guide with three channels, where channel A is offset from channel C by −m degrees and channel B is offset from channel C by +n degrees, assuming the center of channel C aligns with the center of the sensing area of the fingerprint sensor, measured in the same plane as the plane of the sensing area of the fingerprint sensor. «m» and «n» are in the range 0-180 degrees and in some embodiments, m and n are 90 degrees, although it is not necessary that m and n are equal. 
     In addition, when viewed in cross-section, channel C is elevated from the plane of the sensing area of the fingerprint sensor (and hence the plane of channels A and B) by and elevation angle of +p degrees, assuming the center of channel C aligns with the center of the sensing area of the fingerprint sensor, measured in cross section to the plane of the sensing area of the fingerprint sensor. The elevation angle «p» is in the range 0-90 degrees and in various embodiments, p is between 15 and 45 degrees. 
     Various embodiments of angled channels are shown in  FIGS. 60A-60D . In the embodiment shown in  FIG. 60A , channel A is offset from channel C by −90 degrees and channel B is offset from channel C by +90 degrees, while the center of channel C aligns with the center of the sensing area  106  of the fingerprint sensor. As shown in  FIG. 60A , channel C is elevated from the plane of the sensing area  106  by the elevation angle of +40 degrees. In the embodiment shown in  FIG. 60B , channel A is offset from channel C by −45 degrees and channel B is offset from channel C by +45 degrees, while the center of channel C aligns with the center of the sensing area  106  of the fingerprint sensor. As shown in  FIG. 60B , channel C is elevated from the plane of the sensing area  106  by the elevation angle of +20 degrees. In the embodiment shown in  FIG. 60C , channel A is offset from channel C by −135 degrees and channel B is offset from channel C by +135 degrees, while the center of channel C aligns with the center of the sensing area  106  of the fingerprint sensor. As shown in  FIG. 60C , channel C is elevated from the plane of the sensing area  106  by the elevation angle of +20 degrees. In some embodiments, the biometric algorithm is agnostic to rotation. In such embodiments,  FIGS. 60B and 60C  will produce similar images.  FIG. 60D  shows an example of a finger guide configuration with eight channels, seven of which lie in the same plane as the fingerprint sensing area  106  and one of which, i.e., channel C, is angled via the raised section to tip the finger onto the sensing area. In an alternative embodiment described above in  FIGS. 48A and 48B , more than one channel may be angled by using more than one raised section on the base plate to tip the finger in different orientations on the sensing area. 
       FIGS. 61A-61C  show example profiles in cross-section of the raised section and illustrate how angle p of channel C is achieved when the finger is tipped up by hitting the highest edge of the raised section nearest the sensing area  106 . As shown in  FIGS. 61A-61C , various regular and irregular shapes of the raised section are possible and these figures show only a few examples. The raised section may be aligned with the edge of the fingerprint sensor, or may be set back from the edge of the sensor. In  FIG. 61A , the raised section  6102 A is set back from an edge of the sensing area  106 . In  FIG. 61B , an edge of the raised section  6102 B forms a curved shape of the channel wall. In  FIG. 61C , the raised section is set at an edge of the sensing area  106 . 
       FIGS. 62A, 62B, 62C  schematically represent finger contact with a fingerprint sensor using the fingerprint guide of  FIGS. 48A and 48B  according to some embodiments.  FIG. 62A  shows a top plan view of finger contact with the sensing area  106 , where the finger position is represented by arrows A, B, and C. As shown in  FIG. 62A , finger positions A and B are separated by n degrees (e.g., 90 degrees), and finger positions B and C are separated by m degrees (e.g., 90 degrees).  FIG. 62B  shows a side view of a finger contacting the sensing area  106  while positioned on channel B, whereby the finger is oriented at an elevation angle of p degrees (e.g., about 45 degrees).  FIG. 62C  shows a side view of a finger contacting the sensing area while positioned on channel C, whereby the finger is oriented at an elevation angle of q degrees (e.g., about 10-15 degrees). 
       FIG. 63  is a flow chart showing a process  6300  to re-enroll a biometric sensor, such as a fingerprint sensor, based on a trigger event that causes the sensor to go into re-enrollment mode. A process for initially enrolling a biometric such as a fingerprint whereby a trigger event causes the sensor, such as a fingerprint sensor, to enter the enrollment mode is described above and shown in  FIG. 23B . Re-enrollment may be necessary where the initial enrollment was unsuccessful or was only partially successful, resulting in an biometric template incapable of providing reliable verification. A card provider may prohibit re-enrollment entirely for security reasons. 
     In step  6302  of process  6300 , the user connects the biometric sensor-enabled device, such as a fingerprint sensor enabled smart card, for which a biometric template has already been enrolled or an enrollment has been attempted, to a power source, including any of the power sources described above (with or without a finger guide). In step  6304 , a trigger event results in the sensor being put into re-enrollment mode. Exemplary trigger events for re-enrollment at step  6304  may include inserting the card into power source, detecting a specific instance of connecting the card to the power source (e.g., second, third, etc. connection of the smart card to the power source), detection of an existing biometric template already enrolled, detection of certain card inserted into a certain power source (i.e., a known pair), a user is verified by matching finger against existing biometric template, entry of an activation code (i.e., PIN code) (e.g., via a data input template coupled to the power source as described above), a signal from the secure element module or other component of the card, counter of number of uses below a certain threshold (i.e., the user is not permitted to re-enroll if card is not new, or relatively new), age of card below a certain threshold (e.g., memory on card stores a timestamp of when the card was first used in a PoS and a timestamp of when the card was last used and if the difference between the timestamps is less than a certain threshold, re-enrollment is triggered), maximum number of allowable re-enrollments not yet reached, user interactions with the sensor, placing or removing an overlay on the biometric sensor, placing or removing a data input device in the form of an overlay or a sleeve on the biometric sensor, activation of an input mechanism, or any combination of the above. Instead of using a power source, a card provider may trigger re-enrollment if the card is placed in secure terminal, e.g., ATM, PoS or bank terminal. A user ID could then be verified via fingerprint and/or activation code (PIN) or other ID forms as a trigger for re-enrollment. 
     In step  6306 , the user enrolls a fingerprint, e.g., in accordance with any of the enrollment procedures described above. 
     In step  6308 , if the re-enrollment is successful, the existing stored biometric template is replaced in the memory of the host device with a new enrolled biometric template. If the re-enrollment is unsuccessful, then no new biometric template is stored, and the existing biometric template stored in the memory of the host device is retained. Alternatively, in step  6308 , if the re-enrollment is successful, the existing biometric template is modified based on the biometric images acquired during the re-enrollment procedure. For example, the existing biometric template could be enhanced or augmented with additional images, rather than replacing it completely. As part of the process for enhancing or augmenting an existing biometric template, a requirement could be set that new images can only be enrolled to the existing biometric template if they are similar to existing biometric template images (also referred to as a limited form of “dynamic” enrollment.). 
     In step  6310 , the user may remove the smart card from the power source after enrollment of the fingerprint. 
     In some instances, it may be necessary or desirable to enroll a biometric template for each of more than two fingers.  FIG. 64  shows a flow chart illustrating a process  6400  for enrolling a biometric template in a biometric sensor-enabled host device, such as enrolling a fingerprint template in a fingerprint sensor-enabled smart card, whereby after an enrollment process, determination is made as to whether a repeat enrollment procedure should be performed for a different finger. In step  6402 , a fingerprint-enabled smart card is manufactured, and optionally, the manufacturer sets the status of the smartcard as inactive. In step  6404 , the smart card and a power source, e.g., a temporary and removable power source (with or without a finger guide) as described above, is sent to the user. In step  6406 , the user connects the smartcard to the power source. In step  6408 , a trigger event causes the fingerprint sensor to be put into an enrollment mode for a first finger. Exemplary trigger events may include events such as those described above, for example in connection with the process shown in  FIG. 23B . In step  6410 , the user enrolls a fingerprint and if the enrollment is successful, a fingerprint template is created for that finger in the memory of the host device. In step  6412 , a trigger event occurs to determine whether the fingerprint sensor should be put into a repeat enrollment mode for another finger. Trigger event for repeat enrollment at step  6412  could be: a signal from the secure element or other component of the smartcard, detection that the card remains in power source for more than a predetermined number of seconds after last fingerprint template was successfully enrolled, detection of that a number of existing fingerprint templates already enrolled has not yet reached maximum, data entry from user (e.g., the user may hold down an enrolled finger for a long hold on sensor or double tap on sensor, activation code entry), placing or removing an overlay on the sensor, placing or removing a data input device in the form of an overlay or a sleeve on the sensor, activating an input mechanism or any combination of the above. If it is determined at step  6412  that the sensor should be put into a repeat enrollment mode, the sensor returns to step  6410 . If the trigger event does not occur such that the sensor is not put into a repeat enrollment mode, at step  6414 , after enrollment of the required fingers, the user removes the smart card from the power source. In an optional step  6416 , the user contacts the smartcard provider to activate the smartcard. 
     Status Indicators on a Power Source 
     A power source may comprise two or more status indicators (also referred to as indicator elements in the current disclosure). The power source may comprise a receptacle, with or without a finger guide, or the power source may comprise a temporary overlay including a power element, with or without a finger guide. 
     The power source is used only for temporarily providing power to the biometric sensor of the smart card, or other biometric-enabled device, to facilitate enrollment of a biometric verification template. In various embodiments, the power source is not able, and includes no components that would enable the power source, to communicate data to or from any external device other than, in certain embodiments, detecting a status signal from a smart card so that a status indicator may be presented to the user, but without transmitting such signal to any other external device. To thereafter use the biometric sensor for user verification, for example to enable a fingerprint sensor in a smart card to be used for user verification to permit transactions to be completed with the smart card, the smartcard, or other biometric-enabled device, must be uncoupled from the temporary power source and thereafter coupled to an external receiving device capable of transmitting and/or receiving communications (e.g., a point of sale card reader), between the biometric enabled device and the external receiving device. 
     The power source does not provide any capability to transmit data to an external device nor does the power source receive any data from an external device. As such, communication between the power source and any external device is prevented. For example, if the power element of a power source is a socket and the socket is plugged into a main power, the socket is used for power transmission only and power line communication protocols are not used. In addition, the power source does not provide any means to input a biometric template to the smart card or receive a stored biometric template (or a copy of a biometric template) from the smart card. 
     In some embodiments, status indicators comprise LEDs, audio speaker, vibrators, a display, or any combination of the aforementioned. The status indicators may use flashing lights (slow/fast), solid lights (on/off), colored lights, images, text, images, audible tones, vibrations, among others, and/or any combination of the aforementioned, to convey information regarding an enrollment process as shown, for example, in Table 1 below and  FIGS. 69 and 74 . The status indicators may use flashing lights (slow/fast), solid lights (on/off), colored lights (including lights capable of displaying in two or more colors), images, text, images, audible tones, vibrations, among others, and/or any combination of the aforementioned, to instruct a user to place a finger on a fingerprint sensor in a certain direction/position at the appropriate time. The status indicators may convey information regarding the status of the enrollment process to the user while instructing the user to place a finger on a fingerprint sensor in a certain direction/position at the appropriate time 
       FIGS. 65-66  illustrate a device to facilitate enrollment of a verification template of fingerprint data in the form of a power source  6502  comprising two or more status indicators  6504   a - b . In some embodiments, the power source  6502  comprises a receptacle  6510  configured to be removably coupled to a smart card, and the smart card is coupled to the power source  6502  by inserting the smart card into the receptacle  6510  in the direction indicated by printed instructions  6512  included on a surface of the power source  6502 . The printed instructions  6512  included on the surface of the power source  6502  may guide the user as to how to couple and/or decouple the smart card to the power source  6502 . For example, the printed instructions  6512  may comprise text, arrows, and diagrams. In some embodiments, the printed instructions  6512  instruct the user how to enroll their finger and/or inform the user regarding the function of the status indicators. 
     In some embodiments the receptacle  6510  comprises an injection molded plastic frame, a covering layer of artwork and instructions, a PCB  6702 , contact pins  6706 , a signal detection circuit  6708 , and/or support for the power element  6704 , as shown, for example, in  FIGS. 67-68 . The power source  6502  is designed for ease of volume manufacture, low cost and is preferably small and lightweight so that the power source  6502  may be readily transmitted to a user by mail or post. The injection molded plastic frame may be molded as a single piece of plastic and is manufactured with conventional molding tools. The PCB  6702  and the power element  6704  are attached to the injection molded plastic frame. The status indicators  6504   a - b  may be mounted on the PCB  6702 , as shown in  FIG. 67 . The power source includes the power element  6704  which powers the status indicators  6504   a - b . The power element  6704  may be a battery, a solar cell and/or a plug or outlet for connecting to a main power. The PCB  6702  may comprise contact pins  6706  connected to the power element  6704  and the signal detection circuit  6708  and the status indicators  6504   a - b . In such embodiments, the contact pins  6706  make contact with power contact pads of the smart card when the smart card is coupled to the power source  6502 , thereby providing power to the smart card. 
     In some embodiments, the status indicators  6504   a - b  and the signal detection circuit  6708  on the power source are connected to contact pads on the surface of smart card. In such embodiments, the signal detection circuit  6708  may detect a signal from the SE of the smart card regarding a status of the enrollment process. The signal detection circuit  6708  may then signal one or more of the status indicators  6504   a - b  based on the detected status of the enrollment process. The signal detection circuit is open when a smart card is not coupled to the power source and the signal detection circuit is closed when the smart card is coupled to the power source in order to prevent the status indicators from draining the power element. The signal detection circuit may be configured to be open and closed based on the presence of the smart card by using a mechanical switch  6710  which moves when the smart card is coupled to the power source. 
     The signal detection circuit may comprise a voltage comparator configured to detect whether the available voltage of the power element  6704  is below a threshold indicating that the available voltage is not sufficient to power the enrollment process. As described in further detail below, if the voltage is too low, one or more status indicators  6504   a - b  may convey this to the user and/or this state may be signaled to the smart card. 
     As shown in  FIG. 65 , a finger guide  6506  is attached to the receptacle  6510  according to some embodiments. The finger guide  6506  may include two finger guide channels (such as any of the finger guide channels described herein): a first finger guide channel  6508   a  and a second finger guide channel  6508   b . This is not required, however, and the finger guide  6506  may include fewer or more finger guide channels. In some embodiments, a first status indicator  6504   a , for example a green LED, is associated with the first finger guide channel  6508   a  and a second status indicator  6504   b  is associated with the second finger guide channel  6508   b . During enrollment, the status indicators  6504   a - b  instructs the user to place their finger in the direction of the associated finger guide channel in order to capture an image of the finger. The user relies on the status indicators  6504   a - b  to know when and where to apply their finger. The status indicators  6504   a - b  may be used to indicate to the user that enrollment is successful and/or complete. 
     As disclosed herein, the user may apply their finger on each finger guide channel alternately for optimal enrolment. For example, if six images are to be captured with a two-channel finger guide  6506 , the user first goes to position A (e.g., apply a finger in the direction of the first finger guide channel  6508   a ), then position B (e.g., apply the finger in the direction of the second finger guide channel  6508   b ), then position A, then position B, then position A, and then position B. Applying a finger alternately on each channel increases finger movement and increases the likelihood of gathering a sufficient number of different images, thereby providing a high quality template. This exemplary sequence is not required, however, and any sequence of the channel finger guides is possible in alternative embodiments. 
     After enrolling one finger, the user may be permitted to enroll one or more additional fingers according to some embodiments. In such embodiments, a status indicator may signal to the user that the user start enrolling a new finger. As described above, the status indicators associated with each respective channel finger guide instructs and guides the user during enrollment of each new finger. 
     In the context of the present disclosure, a status indicator is “associated” with a finger guide channel if the status indicator and the finger guide channel are constructed and arranged such that there is a one to one correspondence, actual or perceived, between the status indicator and the finger guide channel. For example, and without intending to be limiting, a status indicator may be associated with a finger guide channel by instructional text and/or graphic elements or audible instructions or other signals informing a user that a particular status indicator is associated with a particular finger guide channel, by spatial proximity between the status indicator and the associated finger guide channel, or by physical integration of the status indicator into the associated finger guide channel. 
     As another example, the association between a status indicator and finger guide channel maybe a matter of user perception and may not be the same from one user to the next. For example, for enrolling a fingerprint verification template for a fingerprint-enabled smart card using a temporary power source with status indicators, such as LEDs, associated with different finger guide channels on the power source, users tend to hold the card receptacle of the power source in landscape orientation (i.e., the long dimension of the rectangular card is oriented substantially horizontally) because the user can then read the artwork (text and/or graphic elements) on the receptacle, assuming the artwork is also printed in landscape orientation which is the customary (but not exclusive) orientation for bank cards, bank notes and check books. With the receptacle and card thus oriented, one LED on the receptacle is disposed above the other. That is, the user perceives an “upper” LED and a “lower” LED. Accordingly, the first LED to light up may be the upper LED. Assuming a user is first instructed to place a finger on the fingerprint sensor in the direction of the first finger guide channel  6508   a , when enrolling a right thumb print, it is natural to approach the card from the right-hand side, i.e., to place the thumb in the “correct” finger guide channel (i.e., the finger guide channel  6508   a  next to the active upper LED). However, to enroll a left thumb print, a left-handed user would have to turn the receptacle by ninety degrees straight away for the very first thumb touch to be in the “correct,” or intended, finger guide channel  6508   a . This may feel odd to a new user, and thus, the left-handed user may intuitively put his thumb in the “wrong,” or unintended, finger guide channel (i.e., the finger guide channel  6508   b  nearest to the lower LED which was not lit). A left-handed user trying to enroll a finger may follow the LED lights and alternately hop between the two finger guide channels as desired, but, because of his natural angle of approach, he may consistently place his finger in the “wrong” finger guide channel compared to where the active LED is alight. As long as the user is consistently alternating between the finger guide channels, it may not impact upon the quality of the resulting fingerprint verification template because the order of which finger guide channel starts does not matter. But, in this case, the association of a status indicator with a finger guide channel is a matter of a user&#39;s perception rather than some other associational aspect, such as spatial proximity between the status indicator and the finger guide channel. 
     In another example, the artwork on the power source could be oriented in portrait (i.e., the long dimension of the rectangular card is oriented substantially vertically) so the finger guide is at the bottom with respect to the text on the artwork when a user holds the power source. If the artwork is oriented in this fashion then the user would be more likely to hold the receptacle in portrait orientation and the user would not need to turn the receptacle to obey the first status indicator, regardless of if the user were left or right-handed. Alternatively, a landscape-style power source could be customized for left-handed users to swap the order in which the status indicators come on and/or the sensor may be repositioned in the biometric card. 
     A blind user may choose to hold the power source in a different orientation. The status indicators may be audio rather than visual. In such embodiments, as there is no benefit in seeing the status indicators, the user may turn the power source upside down while enrolling so that the user may more easily feel the finger guide channels. The status indicators may be positioned on a surface of the power source opposite of the surface including the finger guide channels. 
     In an alternative embodiment, the status indicators  6504   a ,  6504   b  may be positioned adjacent one side of the sensor opening as shown, but finger guide channels  6508   a ,  6508   b  may be omitted. The status indicators  6504   a ,  6504   b  may be selectively activated to indicate a position and/or orientation at which a finger should be placed on the sensor without the assistance of a finger guide channel for positioning and orienting the finger. 
     In some embodiments, one or more status indicators may be implemented on the smart card  6806 . In such embodiments, an opening  6802  on the power source  6502  may reveal a status indicator  6804   c  on the smart card  6806  while two status indicators  6804   a - b  are implemented on the power source, as shown in  FIG. 68 . The status indicators  6804   a - c  may be used to display status information during the enrollment process. The status indicators  6804   a - c  may be implemented on the power source  6502 . In some embodiments, any combination of one or more status indicators on the smart card  6806  and the power source  6502  may be used. and the opening  6802  may reveal two more status indicators on the smart card  6806 . In some embodiments, status indicators on the smart card  6806  may be connected to the status indicators on the power source, such that the status indicators on the power source mirror the indications provided to the user by the status indicators on the smart card. The status indicators on the power source may supplement or replace the status indicators on the smart card. 
     A key objective for the system for fingerprint enrollment using the power source as described herein is to prevent any risk of tampering with the smart card and any risk of interfering with or intercepting the enrollment process and/or the components on the smart card. 
     The smart card may signal an enrollment state to the power source during the enrollment process. In some embodiments, status indicators on the power source convey a particular enrollment state to the user during the enrollment process. For example, possible enrollment states that are signaled from the smart card to the power source during the enrollment process are listed below in Table 1.  FIG. 69  lists further possible enrollment states that are signaled from the smart card to the power source and associated status indicators. The list of possible enrollment states shown in  FIG. 69  may be explained with reference to  FIG. 68 . For example, status indicator  6804   a  may correspond to LED “A,” status indicator  6804   b  may correspond to LED “B,” and status indicator  6804   c  may correspond to “Card Green.” 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Possible enrollment state 
                   
               
               
                 (from smart card to power source) 
                 Comment 
               
               
                   
               
             
            
               
                 Wait for finger on (optionally this 
                 Waiting for finger to go down 
               
               
                 is indicated next to the finger 
               
               
                 guide channel required) 
               
               
                 Wait for finger off 
                 Signal user to lift finger off the 
               
               
                   
                 sensor before next image is taken 
               
               
                 Additional finger 
                 Optional indicator for user to enroll a 
               
               
                   
                 second, third, etc. finger on the card 
               
               
                 Acceptable image 
               
               
                 Unacceptable image 
                 Optional. (Alternative to signaling 
               
               
                   
                 an unacceptable image is simply to 
               
               
                   
                 keep signaling to the user that 
               
               
                   
                 additional images are required.) 
               
               
                 Error 
                 Optional 
               
               
                 Enrollment is complete 
               
               
                   
               
            
           
         
       
     
     In some embodiments, only information regarding the status of the enrollment process is sent from the smart card to the power source during enrollment. Other information, for example, card holder details, the fingerprint template, etc. does not leave the smart card during enrollment. 
     In an example of a power source described herein, the power source includes a receptacle into which a smart card may be inserted, the power source provides power to the smart card inserted into the receptacle, data or signals indicative of the enrollment status of the smart card biometric sensor are provided to the power source by the smart card or are detected in the smart card by detection circuitry in the power source, no data is transmitted from the power source to an external device, and status indicators—such as LED lights—on the receptacle (and, optionally, on the smart card as well) are activated to indicate the enrollment status. The enrollment status indicated may include one or more of the following: the smart card biometric sensor is (or is not) in an enrollment mode, the user should provide a biometric image (e.g., place a finger on the a fingerprint sensor), a biometric image provided by the user is (or is not) accepted, the biometric enrollment template is (or is not) complete, the enrollment mode is terminated. The power source may only provide power to the smart card, or the power source may also include one or more data input keys as described herein for inputting data from the power source to the smart card. The power source may optionally include a finger guide as described herein attached to the receptacle and may optionally include status indicators associated with finger guide channels as described herein for guiding or instructing a user with respect to placement of a finger on a finger guide channel. The power source may optionally include status indicators adjacent to a fingerprint sensor of a smart card inserted into the power source receptacle for guiding or instructing a user with respect to placement of a finger on the sensor, and the finger guide channels may be omitted. 
     In another example of a power source described herein, the power source includes a receptacle into which a smart card may be inserted, the power source provides power to the smart card inserted into the receptacle, no data or signals are provided to the power source by the smart card, no data is transmitted from the power source to an external device, and status indicators—such as LED lights—on the smart card are activated to indicate the enrollment status of the smart card biometric sensor. The enrollment status indicated may include one or more of the following: the smart card biometric sensor is (or is not) in an enrollment mode, the user should provide a biometric image (e.g., place a finger on the a fingerprint sensor), a biometric image provided by the user is (or is not) accepted, the biometric enrollment template is (or is not) complete, the enrollment mode is terminated. The power source may only provide power to the smart card, or the power source may also include one or more data input keys as described herein for inputting data from the power source to the smart card. The power source may optionally include a finger guide as described herein attached to the receptacle and may optionally include status indicators associated with finger guide channels as described herein for guiding or instructing a user with respect to placement of a finger on a finger guide channel. The power source may optionally include status indicators adjacent to a fingerprint sensor of a smart card inserted into the power source receptacle for guiding or instructing a user with respect to placement of a finger on the sensor, and the finger guide channels may be omitted. 
     In instances with smart cards including a Secure Element (SE) in addition to a biometric module, two signaling scenarios with respect to the enrollment process may be provided depending on how the enrollment process is split between the Secure Element, the biometric module, and other components on the smart card. The signaling scenario may be determined based on, and not restricted to, the capability of the SE and security requirements, e.g., whether the biometric module is being utilized for a payment application or an application which requires less security. 
     In a first scenario, biometric template storing and matching is performed entirely by the biometric module. In the first scenario, the biometric module notifies the SE (in accordance with a known and predefined protocol) of an enrollment state during enrollment process. In accordance to the received enrollment state notification, the SE may then send signals high/low on contact pads of the smart card. The contact pads used for the signaling may be the data contact pads or the power contact pads or both. The SE or the biometric module may additionally signal the enrollment state via status indicators on the card. The signal detection circuit on the power source detects the state change based on the high/low signals on the contact pads and may drive the status indicators on the power source accordingly. 
     In a second scenario, biometric template storing and matching is split between the biometric module and the SE. In the second scenario, for example, the template storing is performed on the SE. Accordingly, the SE is involved in the enrollment process in cooperation with the biometric module and therefore aware of the enrollment state during the enrollment process. In accordance to the enrollment state, the SE sends signals high/low on contact pads of the smart card. The contact pads used for signaling may be the data contact pads or the power contact pads or both. The SE or the biometric module may additionally signal the enrollment state via status indicators on the card. The signal detection circuit on the power source detects the state change based on the high/low signals on the contact pads and drives the status indicators on the power source accordingly. 
     If the card does not include a SE, the biometric module may send signals high/low on contact pads of the smart card in accordance to the enrollment state. In some embodiments, any other component on the smart card may send signals high/low on contact pads of the smart card in accordance to the enrollment state. The signal detection circuit on the power source detects the state change based on the high/low signals on the contact pads and drives the status indicators on the power source accordingly. 
     The power source may provide an input signal to the smart card to trigger enrollment mode when the smart card is coupled to the power source. In some embodiments, the smart card is a contact or dual-interface card and the smart card may default into operating according to ISO standards for a card transaction as soon as the smart card receives power (i.e., the smart card enters “contact mode”). In such embodiments, a signal from the power source to the card to trigger the enrollment process is necessary. 
     The power source may signal to the smart card that the power element, e.g., a battery, is low. In some alternative embodiments, the power source may not signal to the smart card that the power element is low. In some embodiments, status indicators may indicate to the user that the power element is low. 
     In some embodiments, contact pads on the surface of the smart card may be used to output signals indicating the enrollment states to the user or to input a signal to the smart card as described above. 
     In some embodiments, contact pads that are conventionally used to input/output data to/from the smart card when the smart card is operating in contact mode during a transaction may be repurposed for input/output during enrolment. For example, one output pad, e.g., the C7 pad, may be connected to a signal detection circuit on the power source to drive two status indicators in order to signal enrollment states according to some embodiments. The two status indicators may be two LEDs, e.g., one green LED and one red LED. In some embodiments, additional output pads may be used to drive additional status indicators, e.g., additional LEDs. 
     In some alternative embodiments, conventionally unused pads, e.g., the C4 pad and the C8 pad, may be used to input/output data to/from the smart card. 
     In alternative embodiments, the power source may not provide any input to the smart card. 
     In some embodiments, components on the smart card may manage power during enrollment depending on the nature of the power element on the power source and the number and nature of status indicators on the power source. For example, if too much current is drawn from the power element, e.g., the battery or solar cell, to power the status indicators and the components on the smart card during enrolment, the power element may drain too quickly. A method of managing power during enrollment may include, for example, power management circuitry or a biometric microcontroller (MCU) transitioning components on the smart card not being used to a low power state and/or reducing the processor speed. Another method of managing power during enrollment may include, for example, power management circuitry or the biometric MCU transitioning components on the smart card to a lower power state when the user does not apply a finger to the smart card for a predetermined period of time after the smart card is coupled to the power source. In such instances, the user may need to recouple the card to the power source in order to restart the enrollment process. 
     In some embodiments, art work on a surface of the power source is used to instruct the user to associate a status indicator on the smart card  7002   a - b  with a particular finger guide channel  7004   a - b  on the power source, as shown in  FIG. 70 . For example, for an LED  7002   a - b  on the smart card that is visible through an opening in the power source receptacle, the artwork on the surface of the power source may include text and arrows pointing from the LED  7002   a - b  to a particular finger guide channel  7104   a - b , respectively, thereby indicating to the user to place a finger on the fingerprint sensor  7006  using the finger guide channel  7004   a - b  associated with the lighted LED  7002   a - b.    
     In another example of a power source described herein, the power source includes a receptacle into which a smart card may be inserted, the power source provides power to the smart card inserted into the receptacle, no data is transmitted from the power source to an external device, and the emissions of optical status indicators—such as LED lights—on the smart card, which may be activated to indicate the enrollment status of the smart card biometric sensor, are detected by photo detectors on the receptacle or are channeled via light pipes on the receptacle, and optical status indicators—such as LED lights or display windows—on the receptacle are activated by the emissions detected by the photo detectors or display light channeled by the light pipes to indicate the enrollment status. The enrollment status indicated may include one or more of the following: the smart card biometric sensor is (or is not) in an enrollment mode, the user should provide a biometric image (e.g., place a finger on the a fingerprint sensor), a biometric image provided by the user is (or is not) accepted, the biometric enrollment template is (or is not) complete, the enrollment mode is terminated. The power source may only provide power to the smart card, or the power source may also include one or more data input keys as described herein for inputting data from the overlay to the smart card. The power source may optionally include a finger guide as described herein attached to the receptacle and may optionally include status indicators associated with finger guide channels as described herein for guiding or instructing a user with respect to placement of a finger on a finger guide channel. The power source may optionally include status indicators adjacent to a fingerprint sensor of a smart card inserted into the power source receptacle for guiding or instructing a user with respect to placement of a finger on the sensor, and the finger guide channels may be omitted. 
     The power source may comprise light pipes  7102   a - b  to route the light signal from the status indicators  7104   a - b  on the smart card, e.g., LEDs, to a position on the surface of the power source receptacle, such as a display window  7110   a - b  adjacent to the associated finger guide channel on the power source at the appropriate time, as shown in  FIG. 71 . For example, an LED  7104   a  on the smart card may be illuminated and the associated light pipe  7102   a  may extend the light signal from the LED  7104   a  to the associated finger guide channel  7106   a , thereby indicating to the user to place a finger on the fingerprint sensor  7108  using the associated finger guide channel  7106   a . (Optionally, the input end of the light pipes  7110   a - b  are located on a PCB  6702  (not shown in  FIG. 71 ) of the power source under an external cover panel, facing the surface of the smart card including the one or more status indicators  7104   a - b  and thus the light pipes are exposed to relatively low levels of ambient light making them better able to channel the light emissions from the status indicators  7104   a - b  to the display windows that are visible to the user.) The light pipes  7102   a - b  may extend from a status indicator  7104   a - b  to a display window  7110   a - b  that contacts or covers a portion of the associated finger guide channel. 
     The power source comprises one or more photo detectors (e.g., photodiodes)  7202   a - b  configured to detect illumination emitted by each of the status indicators  7204   a - b  on the smart card and trigger status indicators  7208   a - b  on the power source to highlight the associated finger guide channel  7206   a - b , thereby indicating to the user to place a finger on the fingerprint sensor  7212  using the associated finger guide channel at the appropriate time, as shown in  FIG. 72A . In some embodiments, the one or more photo detectors  7202   a - b  are located on a PCB  6702  (not shown in  FIG. 72A ) of the power source under an external cover panel  7214  (e.g., the artwork), each photo detector  7202   a - b  located adjacent to a separate status indicator  7204   a - b . As shown in  FIG. 72A , the power source comprises a cutout for each status indicator on the smart card so that the status indicators may be revealed to the user. 
       FIGS. 72B-C  show another embodiment of the power source with an external cover panel on the receptacle—which may be printed with instructions, graphics, logos, or other artwork—omitted to illustrate internal features of the power source. The power source comprises one or more photo detectors  7202   a - c  configured to detect the status indicators  7204   a - c  on the smart card  6806 .  FIG. 72B  shows the smart card  6806  including three status indicators  7204   a - c  and the power source including three photo detectors  7202   a - c , each photo detector associated with a separate status indicator. This is not required, however, and the smart card  6806  may include any number of status indicators with the power source including a corresponding number of photo detectors.  FIG. 72B  illustrates the receptacle  6510  of the power source into which the smart card  6806  is inserted, with the PCB  6702  omitted from the figure for the purpose of explanation.  FIG. 72C  illustrates the power source including the PCB  6702  and the inserted smart card  6806 . 
     Referring to  FIG. 72B , the receptacle  6510  is configured with an opening that aligns with the status indicators  7204   a - c  of the card  6806  when the card is fully inserted into the receptacle such that the one or more status indicators  7204   a - c  are not covered by the receptacle  6510 . 
     As shown in  FIG. 72C , the PCB  6702  is mounted within the receptacle  6510 . In some embodiments, the photo detectors  7202   a - c  are located on a surface of the PCB  6702  facing the surface of the smart card including the one or more status indicators  7204   a - c  and thus the photo detectors  7202   a - c  are exposed to relatively low levels of ambient light making them more sensitive to light emissions from the status indicators  7204   a - c . In an embodiment, each of the photo detectors  7202   a - c  is associated with and detects emissions from one of the status indicators  7204   a - c . For example, photo detector  7202   a  is associated with status indicator  7204   a , photo detector  7202   b  is associated with status indicator  7202   b , and photo detector  7202   c  is associated with status indicator  7202   c . Ideally, the photo detectors  7202   a - c  are positioned with respect to their associated status indicators  7204   a - c  and their triggering threshold (i.e., the level of light emission that will trigger a positive detection) are set appropriately, to ensure that photo detectors are not triggered by light bleeding from neighboring, un associated status indicators. In some embodiments, the status indicators  7204   a - c  on the smart card are separated from each other by a distance of at least 3.5 mm such that a light emitting from neighboring, unassociated status indicators is minimized. 
     The PCB  6702  further comprises a decoder and power circuitry  7210  connecting the photo detectors  7202   a - b  to the power source (e.g., a battery  6704 ) and to each associated status indicator  7208   a - b  on the power source. In some embodiments, the decoder detects a signal from a photo detector  7202   a - c  when the photo detector  7202   a - c  is triggered by the illumination of the associated status indicator  7204   a - c  on the smart card. Accordingly, the decoder may decode a status of the enrollment process being signaled by the smart card via the status indicators. For example, the decoder may decode a sequence of signals indicated by the status indicators  7204   a - c  into any number of states regarding the enrollment process. As another non-limiting example, when the smart card includes three status indicators  7204   a - c , the decoder may detect the illuminance of each status indicator, i.e., signaling indicated by the status indicators, using three associated photo detectors  7202   a - c  and the decoder may comprise a binary decoder to decode the signaling indicated by the three status indicators  7204   a - c  into eight different states regarding the enrollment process. The decoder may then trigger one or more status indicators  7208   a - b  on the power source based on the decoded status of the enrollment process. 
     The status indicators on the smart card  6806  and/or the power source  6510  may be bicolor. For example, the status indicators  7208   a - b  on the power source  6510  may be bicolor. The bicolor status indicators may be used to display indications in a particular color, e.g., yellow, when the user is being instructed to apply a certain finger, e.g., a right index finger or a right thumb, and display indications in a different color, e.g., green, when the user is being instructed to apply a different finger, e.g., a left index finger or a left thumb. 
     The three embodiments described above with reference to  FIGS. 70, 71, and 72A -C do not require signals to leave the smart card via the contact pads. Accordingly, there is no need for the biometric module, secure element, or any other component on the smart card to provide a signal that leaves the smart card in the three embodiments described above. Equally, there is no need for the power source to transmit any signal to any external device. 
     In alternative embodiments, the power sources shown in  FIGS. 70, 71, and 72A-72C  may be provided without finger guide channels. In such embodiments, the arrows of  FIG. 70 , the display windows  7110   a ,  7110   b  of  FIG. 71 , or the status indicator lights  7208   a ,  7208   b  of  FIGS. 72A and 72C  are positioned adjacent a side of the sensor opening as shown, but finger guide channels  7004   a ,  7004   b ,  7106   a ,  7106   b ,  7206   a ,  7206   b  may be omitted. The arrows of  FIG. 70 , the display windows  7110   a ,  7110   b  of  FIG. 71 , and the status indicator lights  7208   a ,  7208   b  of  FIGS. 72A and 72C  indicate a position and/or orientation at which a finger should be placed on the sensor without the assistance of a finger guide channel for positioning and orienting the finger. 
     The enrollment process may require an initial enrollment of two fingers. For example, a user may be required to enroll a left thumb and a right thumb. In such embodiments, the power source may comprise at least four status indicators  7302   a - b ,  7404   a - b , as shown in  FIG. 73 . The smart card may comprise two status indicators  7302   a - b . In such embodiments, the power source  6502  may comprise two cutouts where each cutout is positioned over one of the two status indicators  7302   a - b  implemented on the smart card. Printed instructions may be provided on the surface of the power source  6502  to provide guidance to the user with respect to the function of each status indicator. For example, the printed instructions may indicate to the user that one status indicator  7302   a  lights up when the user is required to apply a finger from the left hand and that one status indicator  7302   b  lights up when the user is required by apply a finger from the right hand. In another example, the printed instruction may simply indicate that one status indicator  7302   a  lights up when the user is required to apply a finger from any hand and that one status indicator  7302   b  lights up when the user is required to apply any other finger. As described above, each of the status indicators  7304   a - b  lights up to indicate to the user to position a finger on the associated finger guide channel  7306   a - b . As such, each status indicator  7302   a - b ,  7304   a - b  represents an immediate physical direction cue for the user. Possible states that may be signaled from the smart card to the power source during the two finger enrollment are illustrated in  FIG. 74  according to one embodiment. In the embodiment shown in  FIG. 74 , the “Left” column reflects the indication of the status indicator  7302   a , the “Right” column reflects the indication of the status indicator  7302   b , the “A” column reflects the indication of the status indicator  7306   a , and the “B” column reflects the indication of the status indicator  7306   b , as shown in  FIG. 73 . 
     The photo detectors, light pipes, detector circuits, decoders, and/or finger guide status indicators described herein may also be incorporated in to an overlay, such as overlays shown in  FIGS. 34A-34F and 35  and described above. Finger guide status indicator could be implemented with or without finger guides as described herein. 
     Thus, in another example of an overlay described herein, the overlay provides power to the smart card to which the overlay is applied, no data is transmitted from the overlay to an external device, and the emissions of optical status indicators—such as LED lights—on the smart card, which may be activated to indicate the enrollment status of the smart card biometric sensor, are detected by photo detectors on the receptacle or are channeled via light pipes on the overlay, and optical status indicators—such as LED lights or display windows—on the overlay are activated by the emissions detected by the photo detectors or display windows on the overlay display light channeled by the light pipes to indicate the enrollment status. The enrollment status indicated may include one or more of the following: the smart card biometric sensor is (or is not) in an enrollment mode, the user should provide a biometric image (e.g., place a finger on the a fingerprint sensor), a biometric image provided by the user is (or is not) accepted, the biometric enrollment template is (or is not) complete, the enrollment mode is terminated. The overlay may only provide power to the smart card, or the overlay may also include one or more data input keys as described herein for inputting data from the overlay to the smart card. The overlay may optionally include a finger guide as described herein attached to the overlay and may optionally include status indicators associated with finger guide channels as described herein for guiding or instructing a user with respect to placement of a finger on a finger guide channel. The overlay may optionally include status indicators adjacent to a fingerprint sensor of a smart card to which the overlay is applied for guiding or instructing a user with respect to placement of a finger on the sensor, and the finger guide channels may be omitted. 
     A novel feature of embodiments described herein is the ability to use a fingerprint sensor in a position sensing mode on a limited device such as a smart card. The conventional use of a fingerprint sensor in position sensing mode has been reserved for smart phones, computers and tablets. 
     Another novel feature of embodiments described herein is the different configurations of data input devices, such as data input devices in the form of overlays and frames, temporarily placed over the sensing area of a fingerprint sensor installed on a limited device in order to guide a user to spatially distinct control areas for control and data entry for the device. Once the data input device is removed, the fingerprint sensor operates as a verification method for authorized use of the device. 
     Another novel feature of embodiments described herein is the simple, cost-effective method to enroll a fingerprint template on a limited device using the different configurations of data input devices, such as data input device in the form of overlays and frames, temporarily placed over the sensing area of a fingerprint sensor. 
     One of the significant advantages achieved by embodiments described herein is that the user&#39;s fingerprint data never leaves the smart card. The power source (also referred to as a non-data-transmitting power source) simply provides power to operate the smart card and takes no part in the enrollment process by transmitting data to or from the smart card. Another significant advantage provided by embodiments described herein is that the fingerprint sensor can provide a mechanism for data entry and control of the limited device in addition to user verification. 
     Embodiments described herein provide the user with a convenient method of enrolling a fingerprint while enhancing the security because the enrollment process can be carried out in their home and entirely “off-grid.” A further benefit is the suitability of the process for devices for enrolling fingerprint templates on devices with limited feedback/input capabilities. 
     Exemplary Embodiments 
     Aspects of the disclosure are summarized by the following numbered embodiments. 
     Embodiment 1 
     A fingerprint sensor and data input system comprising: 
     a two-dimensional array of sensor elements, each sensor element being configured to generate a signal in response to a finger surface placed in detectable proximity to the sensor elements; and 
     a processor configured to process signals generated by the sensor elements and to be selectively placed in a fingerprint sensing mode and a data input mode, wherein 
     in the data input mode, the processor is configured to determine in which of two or more spatially distinct regions of the array each sensor element that generates a signal in response to a finger surface placed in detectable proximity to the sensor element is located to effect a data input based on which spatially distinct region is contacted by the finger surface, and 
     in the fingerprint sensing mode, the processor is configured to detect variations in signals generated by sensor elements in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface and to form an image of the fingerprint of the finger surface. 
     Embodiment 2 
     The fingerprint sensor and data input system of embodiment 1, wherein, in the fingerprint sensing mode, the processor is further configured to detect variations in signals generated by sensor elements in detectable proximity to the finger surface that are indicative of features of the fingerprint of the finger surface in each of the two or more spatially distinct regions of the array. 
     Embodiment 3 
     The fingerprint sensor and data input system of embodiment 1, wherein the processor is further configured to detect different interactions of the finger surface with the two-dimensional array of sensor elements, wherein the different interactions of the finger surface with the two-dimensional array of sensor elements include a double tap, a hold, and a drag motion in a direction along the array. 
     Embodiment 4 
     The fingerprint sensor and data input system of embodiment 3, wherein the processor is further configured to switch between the data input mode and the fingerprint sensing mode based on the detected different interactions of the finger surface with the two-dimensional array of sensor elements. 
     Embodiment 5 
     The fingerprint sensor and data input system of any one of embodiments 1 to 4, wherein the two or more spatially distinct regions of the array are permanently indicated on a surface of the two-dimensional array of sensor elements. 
     Embodiment 6 
     The fingerprint sensor and data input system of any one of embodiments 1 to 5, wherein, in the data input mode, the processor is further configured to: 
     calculate an average signal measurement at each of the sensor elements, 
     determine a threshold signal measurement based on the average signal measurement, and 
     determine that a sensor element is contacted by the finger surface when the signal generated by the sensor element exceeds the threshold signal measurement. 
     Embodiment 7 
     The fingerprint sensor and data input system of embodiment 6, wherein, in the data input mode, the processor is further configured to: 
     determine that one or more sensor elements contacted by the finger surface are confined within one spatially distinct region of the array, and 
     determine that the one spatially distinct region of the array is contacted by the finger surface. 
     Embodiment 8 
     The fingerprint sensor and data input system of any one of embodiments 1 to 7, wherein, in the data input mode, sensor elements are selectively enabled to generate signals in response to the finger surface placed in detectable proximity to the selectively enabled sensor elements. 
     Embodiment 9 
     The fingerprint sensor and data input system of embodiment 8, wherein, in the data input mode, sensor elements confined in the two or more spatially distinct regions of the array are selectively enabled. 
     Embodiment 10 
     A fingerprint sensor and data input system comprising: 
     a two-dimensional array of sensor elements, each sensor element being configured to generate a signal in response to a finger surface placed in detectable proximity to the sensor element; 
     a data input device operatively placed on the array and defining two or more spatially distinct regions of the array; and 
     a processor configured to detect and distinguish contact with each of the two or more spatially distinct regions of the array when the data input device is operatively placed on the array and to detect variations in signals generated by sensor elements in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface and to form an image of the fingerprint of the finger surface when the data input device is not operatively placed on the array. 
     Embodiment 11 
     The fingerprint sensor and data input system of embodiment 10, wherein the processor is further configured to form an image of the fingerprint of the finger surface when the data input device is operatively placed on the array. 
     Embodiment 12 
     The fingerprint sensor and data input system of embodiment 10, wherein the data input device comprises two or more windows, the two or more windows defining the two or more spatially distinct regions of the array. 
     Embodiment 13 
     The fingerprint sensor and data input system of any one of embodiments 10 to 12, wherein sensor elements confined in the two or more spatially distinct regions of the array are selectively enabled to generate signals in response to the finger surface placed in detectable proximity to the selectively enabled sensor elements. 
     Embodiment 14 
     The fingerprint sensor and data input system of any one of embodiments 10 to 13, wherein 
     the data input device includes a conductive component which contacts the surface of the array, and 
     the processor is further configured to detect the conductive component when placed in detectable proximity to the two-dimensional array of sensor elements. 
     Embodiment 15 
     The fingerprint sensor and data input system of embodiment 14, wherein the processor is further configured to determine whether the data input device is operatively placed on the array based on the detection of the conductive component. 
     Embodiment 16 
     The fingerprint sensor and data input system of embodiment 15, wherein the processor is further configured to: 
     compare a position of the detected conductive component with an expected position of the detected conductive component when the data input device is operatively placed on the array, and 
     determine whether the data input device is misaligned with the array based on the comparison. 
     Embodiment 17 
     The fingerprint sensor and data input system of embodiment 16, wherein the processor is further configured to calibrate for the misalignment of the data input device when determining whether a finger surface is proximate to the spatially distinct regions. 
     Embodiment 18 
     The fingerprint sensor and data input system of any one of embodiments 14 to 17, wherein 
     the conductive component is arranged on the data input device in a predetermined pattern, the predetermined pattern being a unique pattern associated with the data input device, and 
     the processor is further configured to detect the predetermined pattern and recognize the predetermined pattern as associated with the data input device. 
     Embodiment 19 
     The fingerprint sensor and data input system of any one of embodiments 14 to 18, wherein the conductive component is arranged on the data input device as a pattern, a bar code, a line, a dot, or a cross. 
     Embodiment 20 
     The fingerprint sensor and data input system of any one of embodiments 14 to 19, wherein the conductive component comprises a metal, metalized paint, or conductive ink. 
     Embodiment 21 
     The fingerprint sensor and data input system of any one of embodiments 10 to 20, wherein the data input device comprises an adhesively-backed sticker or film. 
     Embodiment 22 
     The fingerprint sensor and data input system of embodiment 21, wherein the data input device is removably secured to the array. 
     Embodiment 23 
     The fingerprint sensor and data input system of any one of embodiments 10 to 20, wherein the data input device comprises a sleeve configured to be slid over the fingerprint sensor to be operatively placed on the array. 
     Embodiment 24 
     The fingerprint sensor and data input system of embodiment 23, wherein the sleeve is configured to be flipped or slid over the fingerprint sensor to be operatively placed on the array, defining a different two or more spatially distinct regions of the array. 
     Embodiment 25 
     The fingerprint sensor and data input system of embodiment 23 or 24, wherein the sleeve includes a power source and contacts configured to transmit power to the fingerprint sensor when the sleeve is slid over the fingerprint sensor. 
     Embodiment 26 
     The fingerprint sensor and data input system of any one of embodiments 10 to 25, wherein the two or more spatially distinct regions of the array do not constitute the entire two-dimensional array of sensor elements. 
     Embodiment 27 
     The fingerprint sensor and data input system of any one of embodiments 10 to 26, wherein the data input device comprises an upper sheet and a lower sheet, the upper sheet comprising holes defining the two or more spatially distinct regions of the array and the lower sheet comprising a thin continuous material through which the finger surface is detected. 
     Embodiment 28 
     The fingerprint sensor and data input system of embodiment 27, wherein the thin continuous material is polymer and has a thickness of about less than 100 microns. 
     Embodiment 29 
     The fingerprint sensor and data input system of embodiment 27 or 28, wherein the lower sheet has printed, etched, or textured indications to the user positioned to show through the holes of the upper sheet when the lower sheet is combined with the upper sheet. 
     Embodiment 30 
     A fingerprint sensor and data input system comprising: 
     a two-dimensional array of sensor elements, each sensor element being configured to generate a signal in response to a finger surface placed in detectable proximity to the sensor element; 
     a data input device operatively placed on the array and defining two or more spatially distinct regions of the array; and 
     a processor configured to detect and distinguish contact with each of the two or more spatially distinct regions of the array and to detect an activation code entered by a user contacting the two or more spatially distinct regions in a specified sequence when the data input device is operatively placed on the array and to detect variations in signals generated by sensor elements in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface and to form an image of the fingerprint of the finger surface after a correct activation code has been detected. 
     Embodiment 31 
     The fingerprint sensor and data input system of embodiment 30, wherein the processor is configured to distinguish each separate input in the specified sequence for the activation code entered by the user based on an absence of signals generated by sensor elements in the array in between each data input. 
     Embodiment 32 
     The fingerprint sensor and data input system of embodiment 30, wherein the processor is configured to detect a data input by the user simultaneously contacting two or more spatially distinct regions. 
     Embodiment 33 
     The fingerprint sensor and data input system of embodiment 30, wherein 
     the data input device comprises a pattern of windows defining spatially distinct regions of the array corresponding to the pattern of windows, and 
     the activation code requires the user to contact all of the spatially distinct regions of the array corresponding to the pattern of windows simultaneously. 
     Embodiment 34 
     The fingerprint sensor and data input system of embodiment 30, wherein the activation code is an input gesture requiring the user to swipe a pattern connecting two or more spatially distinct regions in a predetermined sequence. 
     Embodiment 35 
     The fingerprint sensor and data input system of any one of embodiments 30 to 34, wherein the processor is configured to detect a valid or invalid data input for the activation code. 
     Embodiment 36 
     The fingerprint sensor and data input system of any one of embodiments 30 to 35, further comprising a status indicator, wherein the status indicator provides an indication to the user regarding the detected valid or invalid data input. 
     Embodiment 37 
     The fingerprint sensor and data input system of embodiment 35, wherein the status indicator is an LED, a screen, or a sound emitting unit. 
     Embodiment 38 
     A method for enrolling a fingerprint with two-dimensional array of sensor elements, each sensor element being configured to generate a signal in response to a finger surface placed in detectable proximity to the sensor element, the method comprising: 
     detecting contact by a user&#39;s finger with different spatially distinct regions of the array of sensor elements; 
     detecting a code entered by the user contacting different spatially distinct regions of the array in a sequence, and authenticating the detected code if it matches a predefined activation code; and 
     if the detected code matches the predefined activation code, storing one or more fingerprint images formed when the user places a finger on the array of sensor elements. 
     Embodiment 39 
     The method of embodiment 38, wherein the code entered by the user comprises data input by simultaneously contacting two or more of the different spatially distinct regions of the array. 
     Embodiment 40 
     The method of embodiment 38, wherein the code entered by the user is a continuous input connecting two or more of the different spatially distinct regions of the array in a pattern. 
     Embodiment 41 
     The method of embodiment 40, further comprising authenticating the detected code if the pattern matches a predefined activation pattern. 
     Embodiment 42 
     The method of any of embodiments 38 to 41, further comprising: 
     alerting the user when the detected code does not match the predefined activation code; and 
     terminating the enrollment method after a predetermined number of failed matches. 
     Embodiment 43 
     The method of any one of embodiments 38 to 42, wherein the two-dimensional array of sensor elements is located on a smart card. 
     Embodiment 44 
     A method for enrolling a fingerprint on a smart card containing a fingerprint sensor comprising: 
     inserting the smart card into a card reader with a power source; 
     entering an activation code by using a finger to contact spatially distinct regions of a sensing area of the fingerprint sensor in a sequence, wherein the spatially distinct regions of the sensing area are defined by a data input device operatively placed on the sensing area; 
     removing the data input device to reveal the entire sensing area of the fingerprint sensor; 
     repeatedly contacting, using the finger, the sensing area of the fingerprint sensor until sufficient images of the finger have been captured to generate a fingerprint template; and 
     removing the smart card from the card reader. 
     Embodiment 45 
     The method of embodiment 44, wherein the entered activation code comprises a data input by simultaneously contacting two or more of the spatially distinct regions of the sensing area. 
     Embodiment 46 
     The method of embodiments 44 or 45, wherein the entered activation code is authenticated if it matches a predefined activation code. 
     Embodiment 47 
     The method of embodiment 44, wherein the entered activation code is a continuous input connecting two or more of the spatially distinct regions of the sensing area in a pattern. 
     Embodiment 48 
     The method of embodiment 47, wherein the entered activation code is authenticated if the pattern matches a predefined activation pattern. 
     Embodiment 49 
     A device comprising: 
     a sensor with a removable data input device over the sensor, the removable data input device comprising a pattern of windows defining spatially distinct regions of the sensor. 
     Embodiment 50 
     The device of embodiment 49, wherein the device is a smart card. 
     Embodiment 51 
     The device of embodiment 49 or 50, wherein the sensor comprises a fingerprint sensor. 
     Embodiment 52 
     A fingerprint sensor and data input system comprising: 
     a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element; 
     a data input device operatively coupled to the array and including two or more data input keys, each key being associated with one or more spatially distinct data input regions of the array; and 
     a processor configured to detect and distinguish contact with each data input key via a signal produced by the one or more spatially distinct data input regions of the array associated with that data input key when the data input device is operatively coupled to the array and to detect variations in signals produced by sensor elements in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface and to form an image of the fingerprint of the finger surface when the data input device is not operatively coupled to the array. 
     Embodiment 53 
     The fingerprint sensor and data input system of embodiment 52, wherein the plurality of sensor elements arranged in the two-dimensional array comprises a plurality of spaced apart drives lines and a plurality of spaced apart pickup lines arranged transversely to the drive lines and separated from the drive lines by a layer of dielectric material. 
     Embodiment 54 
     The fingerprint sensor and data input system of embodiment 52, wherein the plurality of sensor elements arranged in the two-dimensional array comprises a first plurality of spaced apart conductive lines and a second plurality of spaced apart conductive lines arranged transversely to the first plurality of spaced apart conductive lines, wherein each conductive line of the first plurality of spaced apart conductive lines is configured to transmit a signal to the finger surface placed in detectable proximity and each conductive line of the second plurality of spaced apart conductive lines is configured to receive a resultant signal. 
     Embodiment 55 
     The fingerprint sensor and data input system of embodiments 52 to 54, wherein each data input key is electrically connected to the associated spatially distinct data input region of the array. 
     Embodiment 56 
     The fingerprint sensor and data input system of embodiments 52 to 55, wherein each data input key comprises: 
     one or more electrically conductive key traces remotely disposed with respect to the sensor array and configured to be selectively touched by a user finger; 
     one or more conductive sensing area activation traces, each sensing activation trace being disposed in detectable proximity to one data input region of the array; and 
     a conductive connecting trace electrically connecting each of the one or more electrically conductive key traces with one of the sensing area activation traces. 
     Embodiment 57 
     The fingerprint sensor and data input system of embodiment 56, wherein the one or more electrically conductive key traces comprise conductive material applied on or embedded in the data input device. 
     Embodiment 58 
     The fingerprint sensor and data input system of embodiment 56 or 57, wherein the one or more conductive sensing area activation traces comprise conductive material applied on or embedded in the data input device. 
     Embodiment 59 
     The fingerprint sensor and data input system of any one of embodiments 56 to 58, wherein the connecting trace comprises conductive material applied on or embedded in the data input device. 
     Embodiment 60 
     The fingerprint sensor and data input system of any one of embodiments 52 to 59, wherein the array comprises one or more spatially distinct reference regions not associated with a data input key. 
     Embodiment 61 
     The fingerprint sensor and data input system of embodiment 60, wherein each spatially distinct reference region is positioned adjacent to at least one of the spatially distinct data input regions. 
     Embodiment 62 
     The fingerprint sensor and data input system of embodiment 60, wherein the processor is further configured to derive a signal variation based on a first signal produced from one of the spatially distinct reference regions and a second signal produced from one of the one or more spatially distinct data input regions as a result of contact by the user finger with the associated data input key. 
     Embodiment 63 
     The fingerprint sensor and data input system of embodiment 62, wherein the derivation of the signal variation comprises subtracting the first signal produced from the one reference region from the second signal produced from the one data input region. 
     Embodiment 64 
     The fingerprint sensor and data input system of any one of embodiments 52 to 63, wherein at least one of the data input keys comprises first and second electrically conductive contacts configured to be contacted simultaneously by a finger contacting the data input key, wherein the first electrically conductive contact is associated with a first of the spatially distinct data input regions and the second electrically conductive contact is associated with a second of the spatially distinct data input regions. 
     Embodiment 65 
     The fingerprint sensor and data input system of embodiment 64, wherein the first electrically conductive contact and the second electrically conductive contact are interdigitated conductive plates. 
     Embodiment 66 
     The fingerprint sensor and data input system of embodiment 64 or 65, wherein the processor is further configured to derive a signal variation based on a first signal produced from the first spatially distinct data input region of the array and a second signal produced from the second spatially distinct data input region of the array as a result of contact by the user finger with the data input key. 
     Embodiment 67 
     The fingerprint sensor and data input system of embodiment 66, wherein the derivation of the signal variation comprises subtracting the first signal produced from the first spatially distinct data input region of the array from the second signal produced from the second spatially distinct data input region of the array. 
     Embodiment 68 
     The fingerprint sensor and data input system of embodiments 64 to 67, wherein the first spatially distinct data input region is positioned adjacent to the second spatially distinct data input region. 
     Embodiment 69 
     The fingerprint sensor and data input system of embodiment 53, wherein each of the spatially distinct data input regions is substantially aligned with an orientation of the plurality of spaced apart pickup lines. 
     Embodiment 70 
     The fingerprint sensor and data input system of embodiment 53, wherein each of the spatially distinct data input regions is transverse with an orientation of the plurality of spaced apart pickup lines. 
     Embodiment 71 
     The fingerprint sensor and data input system of any one of embodiments 52 to 70 further comprising a power source temporarily connectable to the sensor elements and the processor. 
     Embodiment 72 
     The fingerprint sensor and data input system of embodiment 71, wherein the power source comprises a battery. 
     Embodiment 73 
     The fingerprint sensor and data input system of embodiment 71, wherein the power source comprises a solar cell. 
     Embodiment 74 
     The fingerprint sensor and data input system of embodiment 73, wherein the solar cell is carried on a portion of the data input device. 
     Embodiment 75 
     A fingerprint sensor and data input system comprising: 
     a fingerprint sensor comprising an array of capacitive sensor elements, each sensor element being configured to produce a contact signal when contacted by a finger; and 
     a data input device configured to be removably attached to a host device incorporating the fingerprint sensor and including two or more data input keys, 
     wherein each data input key is remotely coupled with one or more associated data input regions of the array so that the sensor elements encompassed by the associated data input region produce a contact signal when a user touches the data input key. 
     Embodiment 76 
     The fingerprint sensor and data input system of embodiment 75, wherein the data input device comprises an upper layer and a lower layer, 
     the upper layer comprising a hole associated with each of the two or more data input keys, and 
     the lower layer comprising the two or more data input keys, each data input key electrically connected to the associated data input region of the array. 
     Embodiment 77 
     The fingerprint sensor and data input system of embodiment 75, wherein each data input key comprises: 
     a conductive key trace disposed on a top surface of the data input device, 
     a conductive sensing area activation trace disposed on a bottom surface of the data input device, and 
     a conductive connecting trace extending through the data input device and electrically connecting the key trace with the sensing area activation trace. 
     Embodiment 78 
     The fingerprint sensor and data input system of any one of embodiments 75 to 77, wherein the data input device is removably attached to the host device with a repositionable adhesive. 
     Embodiment 79 
     The fingerprint sensor and data input system of any one of embodiments 75 to 78, wherein the data input device further comprises a conductive positioning feature which contacts the array when the data input device is attached to the host device, wherein the fingerprint sensor is configured to detect the positioning feature, to compare a position of the positioning feature with an expected position of the positioning feature when the data input device is attached to the host device, and to determine the position of the data input device with respect to the array based on the comparison. 
     Embodiment 80 
     The fingerprint sensor and data input system of embodiment 79, wherein the fingerprint sensor is further configured to calibrate positions of the data input regions based on the position of the data input device with respect to the array. 
     Embodiment 81 
     The fingerprint sensor and data input system of embodiment 75, wherein the data input device comprises: 
     a remote keypad device including the two or more data input keys, and 
     a data transfer cable electrically coupling the data input keys electrically to each associated data input region. 
     Embodiment 82 
     The fingerprint sensor and data input system of any one of embodiments 75 to 81, wherein the array of capacitive sensor elements is a two-dimensional array or a one-dimensional array. 
     Embodiment 83 
     A data input system comprising: 
     a host device with a sensor; and 
     a data input device removably disposed over the sensor, the data input device comprising two or more data input keys, wherein each data input key is associated with one or more spatially distinct data input regions of a sensing area of the sensor. 
     Embodiment 84 
     The system of embodiment 83, wherein the host device comprises a smart card. 
     Embodiment 85 
     The system of embodiment 83 or embodiment 84, wherein the sensor comprises a fingerprint sensor. 
     Embodiment 86 
     The system of any one of embodiments 83 to 85, wherein the data input device is wrapped around a portion of the host device containing the sensor so as to cover at least a part of a first surface of the host device in which the sensor is disposed and a second surface of the host device different from the first surface. 
     Embodiment 87 
     The host device of embodiment 86, wherein the data input device comprises at least one data input key on the portion of the data input device covering the first surface and at least one data input key on the portion of the data input device covering the second surface. 
     Embodiment 88 
     A data input device removably attachable with respect to an array of contact sensor elements, said data input device comprising: 
     two or more data input keys remotely disposed with respect to a portion of the data input device covering the array, each data input key comprising a conductive key trace disposed on the data input device; 
     a conductive sensing area activation trace associated with each data input key and configured to be disposed over a spatially discrete portion of the array when the data input device is removably attached with respect to the array, and 
     a conductive connecting trace electrically connecting each conductive key trace with the associated sensing area activation trace. 
     Embodiment 89 
     A method for enrolling a fingerprint on a smart card containing a fingerprint sensor, the method comprising: 
     connecting the smart card to a power source; 
     entering an activation code by using a finger to contact two or more data input keys of a data input device attached to the smart card in a sequence corresponding to the activation code, wherein a portion of the data input device is positioned over a sensing area of the fingerprint sensor and each data input key is associated with one or more spatially distinct data input regions of the sensing area; 
     removing a portion of the data input device from the smart card to uncover the sensing area of the fingerprint sensor; 
     contacting the sensing area of the fingerprint sensor one or more times with a finger to enroll a fingerprint template; and 
     disconnecting the smart card from the power source. 
     Embodiment 90 
     The method of embodiment 89, wherein the entered activation code comprises a data input by simultaneously contacting two or more data input keys. 
     Embodiment 91 
     The method of embodiment 89 or embodiment 90, wherein the power source is a wireless power source configured to wirelessly power the fingerprint sensor, and the connecting step comprises placing the smart card in operative proximity to the wireless power source. 
     Embodiment 92 
     The method of embodiment 89, wherein the data input device comprises the power source, the power source electrically coupled to the fingerprint sensor. 
     Embodiment 93 
     The method of embodiment 92, wherein the power source is a solar cell panel and 
     wherein the step of connecting the smart card to the power source comprises removing an overlay removably placed over the solar cell panel contained in the data input device. 
     Embodiment 94 
     A smart card comprising: 
     a card body capable of deflection along any axis lying in the plane of the card; 
     a fingerprint sensor for authenticating a user of the smart card; 
     a data storage element storing an activation code; 
     a data input device coupled to the fingerprint sensor to associate distinct areas of the data input device with distinct areas of the fingerprint sensor, each distinct area of the sensor corresponding to a uniquely identifiable portion of an activation code; and 
     a processor configured to translate a code input by a user interacting with the fingerprint sensor via the data input device and to compare the code input by the user with the stored activation code. 
     Embodiment 95 
     The smart card of embodiment 94, wherein the fingerprint sensor comprises a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element. 
     Embodiment 96 
     A method for enrolling a fingerprint sensor comprising: 
     defining an activation code to initiate an enrollment process for the fingerprint sensor; and 
     enabling a user to enter the activation code into the fingerprint sensor by interacting with each of two or more distinct portions of the fingerprint sensor, wherein each of the two or more distinct portions of the fingerprint sensor corresponds to a uniquely-identifiable portion of the activation code. 
     Embodiment 97 
     The method of 96, wherein the fingerprint sensor comprises a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element. 
     Embodiment 98 
     A method for enrolling a fingerprint template on a smart card having a fingerprint sensor, said method comprising: 
     connecting one or more power transmission contacts of the smart card to a power source without connecting any data transmission contacts of the smart card to a device configured to transmit or receive data; 
     automatically activating an enrollment mode in the fingerprint sensor upon a specific instance of connecting the one or more power transmission contacts of the smart card to the power source; 
     enrolling a fingerprint by storing a fingerprint template derived from one or more fingerprint images generated by placing a finger on the fingerprint sensor; and 
     upon completion of the enrolling step, automatically deactivating the enrollment mode in the fingerprint sensor. 
     Embodiment 99 
     The method of embodiment 98, further comprising automatically deactivating the enrollment mode in the fingerprint sensor upon disconnecting the one or more power transmission contacts of the smart card from the power source before completing the enrolling step. 
     Embodiment 100 
     The method of embodiment 98 or embodiment 99, further comprising providing a confirming indication that the smart card is in enrollment mode after the specific instance of connecting the one or more power transmission contacts of the smart card to the power source. 
     Embodiment 101 
     The method of embodiment 100, wherein the confirming indication that the smart card is in enrollment mode comprises illuminating a light on the smart card. 
     Embodiment 102 
     The method of any one of embodiments 98 to 101, further comprising providing a confirming indication that the enrolling step is successfully completed. 
     Embodiment 103 
     The method of embodiment 102, wherein the confirming indication that the enrolling step is successfully completed comprises illuminating a light on the smart card. 
     Embodiment 104 
     The method of any one of embodiments 98 to 103, further comprising providing a confirming indication that the one or more power transmission contacts of the smart card are connected to the power source. 
     Embodiment 105 
     The method of embodiment 104, wherein the confirming indication that the one or more power transmission contacts of the smart card are connected to the power source comprises illuminating a light on the smart card. 
     Embodiment 106 
     The method of any one of embodiments 98 to 105, wherein the specific instance is the first instance. 
     Embodiment 107 
     A method for enrolling a fingerprint template on a smart card having a fingerprint sensor, said method comprising; 
     connecting one or more power transmission contacts of the smart card to a power source without connecting any data transmission contacts of the smart card to a device configured to transmit data to or receive data from the smart card; 
     determining if a fingerprint template has been enrolled for the fingerprint sensor of the smart card; 
     if no fingerprint template has been enrolled for the fingerprint sensor of the smart card, automatically activating an enrollment mode in the fingerprint sensor upon connecting the one or more power transmission contacts of the smart card to the power source; 
     enrolling a fingerprint by storing a fingerprint template derived from one or more fingerprint images generated by placing a finger on the fingerprint sensor; and 
     upon completion of the enrolling step, automatically deactivating the enrollment mode in the fingerprint sensor. 
     Embodiment 108 
     The method of embodiment 107, further comprising providing a confirming indication that the smart card is in enrollment mode after the specific instance of connecting the one or more power transmission contacts of the smart card to the power source. 
     Embodiment 109 
     The method of embodiment 108, wherein the confirming indication that the smart card is in enrollment mode comprises illuminating a light on the smart card. 
     Embodiment 110 
     The method of any one of embodiments 107 to 109, further comprising providing a confirming indication that the enrolling step is successfully completed. 
     Embodiment 111 
     The method of embodiment 110, wherein the confirming indication that the enrolling step is successfully completed comprises illuminating a light on the smart card. 
     Embodiment 112 
     The method of any one of embodiments 107 to 111, further comprising providing a confirming indication that the one or more power transmission contacts of the smart card are connected to the power source. 
     Embodiment 113 
     The method of embodiment 112, wherein the confirming indication that the one or more power transmission contacts of the smart card are connected to the power source comprises illuminating a light on the smart card. 
     Embodiment 114 
     The method of any one of embodiments 107 to 113, wherein the specific instance is the first instance. 
     Embodiment 115 
     A fingerprint sensor and data input system comprising: 
     a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element; 
     a data input device, including a portion disposed over the array and including a pattern of piercings formed in the portion of the data input device disposed over the array, wherein the piercings are spatially associated with one or more spatially distinct data input regions of the array; and 
     a processor configured to detect a finger placed in contact with the associated spatially distinct data input regions of the array and to detect a pattern of signals produced by the spatially distinct data input regions contacted through the pattern of piercings. 
     Embodiment 116 
     The fingerprint sensor and data input system of embodiment 115, wherein the processor is further configured to compare the pattern of signals detected with a predefined pattern to determine if the pattern of piercings of the data input device corresponds to the predefined pattern. 
     Embodiment 117 
     A fingerprint sensor and data input system comprising: 
     a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element; 
     a data input device, including a portion disposed over the array and including a pattern of conductive material applied to the portion of the data input device disposed over the array, wherein the pattern is spatially associated with one or more spatially distinct data input regions of the array; and 
     a processor configured to detect contact of the pattern of conductive material with the associated spatially distinct data input regions of the array and to detect a pattern of signals produced by the spatially distinct data input regions contacted by the pattern of conductive material. 
     Embodiment 118 
     The fingerprint sensor and data input system of embodiment 117, wherein the processor is further configured to compare the pattern of signals detected with a predefined pattern to determine if the pattern of conductive material of the data input device corresponds to the predefined pattern. 
     Embodiment 119 
     A fingerprint sensor and data input system comprising: 
     a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element; 
     a data input device partially disposed over the array and including two or more data input keys, each key being associated with one or more spatially distinct data input regions of a first portion of the array, and a cutout exposing a second portion of the array; and 
     a processor configured to detect and distinguish contact with each data input key via a signal produced by the one or more spatially distinct data input regions of the array associated with that data input key and to detect variations in signals produced by sensor elements of the second portion of the array in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface. 
     Embodiment 120 
     The fingerprint sensor and data input system of embodiment 119, wherein each data input key is electrically connected to the associated spatially distinct data input region of the array. 
     Embodiment 121 
     The fingerprint sensor and data input system of embodiment 119 or 120, wherein each data input key comprises: 
     one or more electrically conductive key traces remotely disposed with respect to the first portion of the sensor array and configured to be selectively touched by a user finger; 
     one or more conductive sensing area activation traces, each sensing area activation trace being disposed in detectable proximity to one data input region of the array; and 
     a conductive connecting trace electrically connecting each of the one or more electrically conductive key traces with one of the sensing area activation traces. 
     Embodiment 122 
     The fingerprint sensor and data input system of embodiment 121, wherein the one or more electrically conductive key traces comprise conductive material applied on or embedded in the data input device. 
     Embodiment 123 
     A device including a fingerprint sensor and data input system and comprising: 
     a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element; 
     two or more data input keys disposed on a portion of the device remote from the plurality of sensors, each data input key being coupled with one or more spatially distinct data input regions of a first portion of the array so that contact with the data input key results in a signal produced by sensor elements within each spatially distinct data input region coupled to the data input key; and 
     a processor configured to detect and distinguish contact with each data input key via a signal produced by the one or more spatially distinct data input regions of the array coupled with that data input key and to detect variations in signals produced by sensor elements of a second portion of the array in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface. 
     Embodiment 124 
     A method for enrolling a fingerprint on a smart card containing a fingerprint sensor, the method comprising: 
     connecting the smart card to a power source; 
     entering an activation code by using a finger to contact two or more data input keys of a data input device attached to the smart card in a sequence corresponding to the activation code, wherein a portion of the data input device is positioned over a portion of the sensing area of the fingerprint sensor, and each data input key is associated with one or more spatially distinct data input regions of a portion of the sensing area; 
     contacting the portion of the sensing area of the fingerprint sensor that is not covered by a portion of the data input device one or more times with a finger to enroll a fingerprint template; and 
     disconnecting the smart card from the power source. 
     Embodiment 125 
     A method for enrolling a fingerprint template on a smart card having a fingerprint sensor, said method comprising: 
     connecting one or more power transmission contacts of the smart card to a power source without connecting any data transmission contacts of the smart card to a device configured to transmit or receive data; 
     activating an enrollment mode in the fingerprint sensor upon detection of a trigger event; 
     enrolling a fingerprint by storing a fingerprint template derived from one or more fingerprint images generated by placing a finger on the fingerprint sensor; and 
     upon completion of the enrolling step, deactivating the enrollment mode in the fingerprint sensor. 
     Embodiment 126 
     The method of embodiment 125, wherein the trigger event comprises one or more trigger events selected from the list consisting of:
         a. user interactions with the biometric sensor assembly;   b. placing a detectable object on the biometric sensor assembly;   c. removing a detectable object from the biometric sensor assembly;   d. detecting the absence of a stored verification template;   e. detecting the presence of a stored verification template that is partially complete;   f. detecting that power is being transmitted to the smart card for the first time;   g. detecting a specified instance of power being transmitted to the smart card;   h. detection that a maximum number of unsuccessful attempts to derive a verification template has not been reached;   I. activating an input mechanism;   j. expiration of a timer or counter;   k. occurrence of an error state;   l. detection of a flag set last time the smart card was inserted in a card reader that transmits data to or from the smart card;   m. detection that the smart card has been connected to a power source that does not transmit data to or from the card;   n. detection of a trigger event by a component of the smart card other than the biometric sensor assembly; and   o. detection that a particular smart card has been coupled to a particular non-data-transmitting power source.       

     Embodiment 127 
     A power source for a smart card comprising: 
     a power element; and 
     a housing comprising: 
     a slot configured to receive an end of the smart card; and 
     contacts connected to the power element, wherein the contacts contact power transmission contact pads of the smart card and do not contact data transmission contact pads of the smart card when the smart card is inserted into the slot to thereby connect the power transmission contact pads of the smart card to the power element. 
     Embodiment 128 
     The power source of embodiment 127, wherein the power element is a battery. 
     Embodiment 129 
     The power source of embodiment 127, wherein the power element is a socket on the power source to allow connection to a main power source. 
     Embodiment 130 
     The power source of embodiment 127, wherein the housing is made of plastic. 
     Embodiment 131 
     The power source of embodiment 127, wherein the housing may include one or more status indicators. 
     Embodiment 132 
     The power source of embodiment 131, where the power source further comprises a detector circuit that, responsive to detecting that a component on the smart card has modulated a power line to indicate its state, activates the one or more status indicators to indicate the detected state to a user. 
     Embodiment 133 
     An overlay configured to provide power to an electronic device having terminals for connecting a source of electric power to the electronic device, wherein the overlay is configured to be removably secured to a surface of the electronic device and comprises: 
     a film configured to conform to the surface of the electronic device when secured thereto; 
     a power element supported on the film; 
     conductive material disposed on or embedded in a surface of the film, wherein the conductive material connects the power element to the terminals of the electronic device when the overlay is secured to the surface of the electronic device; and 
     a circuit closure configured to enable a user to selectively close a power circuit between the power element and the terminals of the electronic device to enable power transmission between the power element and the electronic device. 
     Embodiment 134 
     The overlay of embodiment 133, wherein the power element comprises a battery, a solar chip, a USB plug or an NFC transceiver. 
     Embodiment 135 
     The overlay of embodiment 133 or 134, wherein the overlay further includes: 
     a power element contact pad disposed on the film and on which the power element is disposed; and 
     a conductive contact disposed on a portion of the film that is spatially distinct from the power element contact pad, and wherein the conductive material comprises a first power connection trace extending from the power element contact pad to a first terminal of the electronic device and a second power connection trace extending from the conductive contact to a second terminal of the electronic device, and wherein the circuit closure comprises a portion of the film on which the conductive contact is disposed that is foldable so as to place the conductive contact in contact with the power element disposed on the power element contact pad. 
     Embodiment 136 
     The overlay of embodiment 133 or 134, wherein the overlay further includes: 
     a power element contact pad disposed on the film and on which the power element is disposed; and 
     a conductive clip positioned on the film and configured to hold the power element in place on the power element contact pad, and wherein the conductive material comprises a first power connection trace extending from the power element contact pad to a first terminal of the electronic device and a second power connection trace extending from the a portion of the conductive clip to a second terminal of the electronic device, and wherein the circuit closure comprises a non-conductive material disposed between the clip and the power element and which can be removed by a user to complete the power circuit through the power element. 
     Embodiment 137 
     The overlay of any one of embodiments 133 to 136, further comprising an adhesive on a surface of the film for removably securing the film to the surface of the electronic device. 
     Embodiment 138 
     The overlay of any one of embodiments 133 to 137, further comprising: 
     one or more electrically conductive key traces disposed on the film and configured to be selectively touched by a user finger; 
     one or more conductive sensing area activation traces, each sensing area activation trace being disposed on the film in detectable proximity to one data input region of a two-dimensional array of sensor elements of the electronic device, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element; and 
     a conductive connecting trace disposed on the film and electrically connecting each of the one or more electrically conductive key traces with one of the sensing area activation traces. 
     Embodiment 139 
     The overlay of embodiment 138, wherein the film includes a cutout exposing a portion of the array. 
     Embodiment 140 
     The overlay of any one of embodiments 133 to 139, wherein the electronic device is a smart card, and the overlay covers at least a portion of a surface of the smart card. 
     Embodiment 141 
     The overlay of any one of embodiments 133 to 140, wherein the overlay is configured to connect to data transmission terminals of the electronic device. 
     Embodiment 142 
     The overlay of embodiment 141, wherein the overlay enables a wired or wireless communication channel between the data transmission terminals of the electronic device and a second electronic device. 
     Embodiment 143 
     The overlay of embodiment 141 or 142, further comprising status indicators configured to indicate information transmitted to or received from the data transmission terminals. 
     Embodiment 144 
     A method for enrolling a biometric template on an electronic device having power terminals, data transmission terminals and a biometric sensor, the method comprising: 
     connecting an overlay to the electronic device, wherein the overlay is configured to provide power to the electronic device from a power element mounted on the overlay to the power terminals of the electronic device and to connect to the data transmission terminals of the electronic device; 
     closing a power circuit between the power element and the power terminals of the electronic device to enable power transmission between the power element and the electronic device; 
     triggering the biometric sensor to enter an enrollment mode; and 
     generating the biometric template from biometric inputs from a user to the biometric sensor. 
     Embodiment 145 
     A finger guide configured to be removably attached to a device having a fingerprint sensor and comprising two or more channels, wherein each channel is configured to position a finger placed thereon to contact the fingerprint sensor at a different orientation. 
     Embodiment 146 
     The finger guide of embodiment 145, wherein each channel is spaced from each other channel by an angle in the plane of a sensing surface of the fingerprint sensor. 
     Embodiment 147 
     The finger guide of embodiment 145 or 146, wherein at least one channel positions the finger to contact the fingerprint sensor at an elevation angle relative to the plane of the sensing surface. 
     Embodiment 148 
     The finger guide of any one of embodiments 145 to 147, wherein at least two channels position the finger to contact the fingerprint sensor at an elevation angle relative to the plane of the sensing surface and wherein the elevation angle of each of the two channels is different from the other. 
     Embodiment 149 
     The finger guide of any one of embodiments 145 to 148, wherein each channel is spaced 90 degrees from one other channel. 
     Embodiment 150 
     The finger guide of any one of embodiments 145 to 149, comprising a base plate having a surface conforming or conformable to a surface of the device on which the finger guide is removably attached, wherein a removable adhesive is applied to the surface of the base plate. 
     Embodiment 151 
     The finger guide of any one of embodiments 145 to 150, wherein at least one of the channels is formed on a raised section that is adjacent to the fingerprint sensor so that the finger placed on the channel contacts the fingerprint sensor at an elevation angle with respect to a plane of the fingerprint sensor. 
     Embodiment 152 
     The finger guide of embodiment 151, further comprising a front stop disposed on an opposite side of the fingerprint sensor from the raised section. 
     Embodiment 153 
     The finger guide of any one of embodiments 145 to 152, including a cutout formed therein to expose the fingerprint sensor. 
     Embodiment 154 
     The finger guide of any one of embodiments 145 to 153, wherein each channel is formed on a channel wing. 
     Embodiment 155 The finger guide of embodiment 154, wherein at least one channel wing extends beyond an edge of the device when the finger guide is attached to the device in operative proximity to the fingerprint sensor. 
     Embodiment 156 
     The finger guide of any one of embodiments 145 to 155, further comprising a power element to provide a source of electrical power and contacts connected to the power element, wherein the contacts contact power transmission elements of the device when the finger guide is attached to the device to thereby connect the power transmission element of the device to the power element. 
     Embodiment 157 
     The finger guide of any one of embodiments 145 to 156, further comprising a data input device partially disposed over the fingerprint sensor and including two or more data input keys, each data input key being associated with one or more spatially distinct data input regions of the portion of the fingerprint sensor over which the data input device is disposed. 
     Embodiment 158 
     The finger guide of any one of embodiments 146 to 157, wherein the finger guide is configured to be moveable with respect to the fingerprint sensor to selectively place a different one of the channels in operative proximity to the fingerprint sensor. 
     Embodiment 159 
     The finger guide of embodiment 158, wherein the finger guide is linearly movable with respect to the fingerprint sensor. 
     Embodiment 160 
     The finger guide of embodiment 158, wherein the finger guide is rotatable with respect to the fingerprint sensor. 
     Embodiment 161 
     A power source and finger guide for a smart card including a fingerprint sensor comprising: 
     a power element; 
     a card holder frame comprising: 
     one or more card guide rails into which the smart card is inserted to position the cardholder frame with respect to the smart card; and 
     contacts connected to the power element, wherein the contacts contact power transmission contact pads of the smart card when the smart card is inserted into the card guide rail to thereby connect the power transmission contact pads of the smart card to the power element; and 
     a finger guide attached to the card holder frame and comprising two or more channels, wherein each channel is configured to position a finger placed thereon to contact the fingerprint sensor at a different orientation. 
     Embodiment 162 
     A fingerprint sensor and data input system comprising: 
     a plurality of sensor elements arranged in a two-dimensional array, each sensor element being configured to produce a signal in response to a finger surface placed in detectable proximity to the sensor element; 
     a data input device partially disposed over the array and including two or more data input keys, each key being associated with one or more spatially distinct data input regions of a first portion of the array, and a cutout exposing a second portion of the array; 
     a processor configured to detect and distinguish contact with each data input key via a signal produced by the one or more spatially distinct data input regions of the array associated with that data input key and to detect variations in signals produced by sensor elements of the second portion of the array in detectable proximity to the finger surface that are indicative of features of a fingerprint of the finger surface; and 
     finger guide comprising two or more channels, wherein each channel is configured to position a finger placed thereon to contact the two-dimensional array at a different orientation. 
     Embodiment 163 
     A method for enrolling a fingerprint on a smart card containing a fingerprint sensor, the method comprising: 
     connecting the smart card to a power source; 
     entering into an enrollment mode upon determination of a trigger event; 
     contacting the fingerprint sensor by placing the same finger on each of two or more finger guide channels configured to position the finger placed thereon in a unique orientation with respect to the fingerprint sensor to enroll a fingerprint template for that finger; and 
     disconnecting the smart card from the power source after enrolling the fingerprint template. 
     Embodiment 164 
     The method of embodiment 163, wherein the trigger event comprises one or more trigger events selected from the list consisting of:
         a. user interactions with the biometric sensor assembly;   b. placing a detectable object on the biometric sensor assembly;   c. removing a detectable object from the biometric sensor assembly;   d. detecting the absence of a stored verification template;   e. detecting the presence of a stored verification template that is partially complete;   f. detecting that power is being transmitted to the smart card for the first time;   g. detecting a specified instance of power being transmitted to the smart card;   h. detection that a maximum number of unsuccessful attempts to derive a verification template has not been reached;   I. activating an input mechanism;   j. expiration of a timer or counter;   k. occurrence of an error state;   l. detection of a flag set last time the smart card was inserted in a card reader that transmits data to or from the smart card;   m. detection that the smart card has been connected to a power source that does not transmit data to or from the card;   n. detection of a trigger event by a component of the smart card other than the biometric sensor assembly; and   o. detection that a particular smart card has been coupled to a particular non-data-transmitting power source.       

     Embodiment 165 
     The method of embodiment 163 or embodiment 164, wherein enrolling the fingerprint template comprises determining that a specified number of acceptable fingerprint sensor images has been generated for each finger guide channel. 
     Embodiment 166 
     A method for re-enrolling a fingerprint on a smart card containing a fingerprint sensor wherein at least one fingerprint template has been previously enrolled, the method comprising:
         A. connecting the smart card to a power source;   B. entering into a re-enrollment mode upon determination of a trigger event;   C. contacting the fingerprint sensor by sequentially placing the same finger on each of two or more finger guide channels configured to position the finger placed thereon in a unique orientation with respect to the fingerprint sensor to enroll a fingerprint template for that finger;   D. replacing the previously enrolled fingerprint template with a new fingerprint template formed from fingerprint images generated during step C or updating the previously enrolled fingerprint template with fingerprint images generated during step C; and   E. disconnecting the smart card from the power source.       

     Embodiment 167 
     The method of embodiment 166, wherein the trigger event for entering re-enrollment mode comprises one or more of inserting the card into power source, detection of a specific instance of card connection to the power source, detection of an existing fingerprint template already enrolled, detection of a certain card inserted into a certain power source, verifying a user by matching a finger against existing fingerprint template, entry of an activation code, receiving a signal from a secure element module of the card, a counter of number of uses below a certain threshold, the age of card below a certain threshold, a maximum number of allowable re-enrollments not yet reached, user interactions with the sensor, placing or removing an overlay, placing or removing a data input device in the form of an overlay or a sleeve on the biometric sensor, and activation of an input mechanism. 
     Embodiment 168 
     A method for enrolling two or more fingerprints on a device containing a fingerprint sensor, the method comprising:
         A. connecting the device to a power source;   B. entering into a first enrollment mode upon determination of a trigger event;   C. enrolling a first fingerprint template for a first finger,   D. entering a subsequent enrollment mode upon determination of a trigger event;   E. enrolling a subsequent fingerprint template for a subsequent finger different from a previously enrolled finger;   F. determining if a required number of fingers has been enrolled;   G. if the required number of fingers has not been enrolled, return to step D; and   H. if the required number of fingers has been enrolled, disconnecting the smart card from the power source.       

     Embodiment 169 
     A system for enrolling a verification template of biometric data in a biometric-enabled smart card, the system comprising: 
     a non-data-transmitting power source configured to be coupled to the smart card to transmit power to the smart card without transmitting data to or from the smart card, wherein the non-data-transmitting power source comprises a power element and a receptacle configured to receive an end of the smart card; and 
     a biometric sensor assembly comprising one or more sensor elements and associated circuitry for controlling operation of the one or more sensor elements and for processing signals from the one or more sensor elements, 
     wherein the biometric sensor assembly is configured to be installed in the smart card whereby power is transmitted to the biometric sensor assembly when the non-data-transmitting power source is coupled to the smart card, 
     wherein the biometric sensor assembly is configured to operate in an enrollment mode when power is transmitted to the biometric sensor assembly by the non-data-transmitting power source, and 
     wherein, when operating in enrollment mode, the biometric sensor assembly is configured to derive and store a verification template of biometric data from one or more biometric images generated by the one or more sensor elements. 
     Embodiment 170 
     The system of Embodiment 169, wherein the biometric sensor assembly is configured to operate in an enrollment mode when the non-data-transmitting power source is coupled to the smart card and power is transmitted to the biometric sensor assembly combined with the occurrence of a trigger event. 
     Embodiment 171 
     The system of Embodiment 169 or Embodiment 170, wherein the biometric sensor assembly is configured to terminate enrollment mode when the non-data-transmitting power source is uncoupled from the smart card and power is no longer transmitted to the biometric sensor assembly. 
     Embodiment 172 
     The system of Embodiment 169 or Embodiment 170, wherein the biometric sensor assembly is configured to terminate enrollment mode after the verification template of biometric data is stored. 
     Embodiment 173 
     The system any one of Embodiments 169 to 172, wherein the biometric sensor assembly comprises a fingerprint sensor, and the verification template is derived from one or more fingerprint images. 
     Embodiment 174 
     The system of any one of Embodiments 169 to 173, wherein the non-data-transmitting power source comprises one or more terminals configured to contact one or more corresponding power transmission contacts of the smart card when the non-data-transmitting power source is coupled to the smart card, and wherein the non-data-transmitting power source lacks any terminals contacting data transmission contacts of the smart card when the non-data-transmitting power source is coupled to the smart card. 
     Embodiment 175 
     The system of Embodiment 170, wherein the trigger event comprises one or more trigger events selected from the group consisting of:
         a. user interactions with the biometric sensor assembly;   b. placing a detectable object on the biometric sensor assembly;   c. removing a detectable object from the biometric sensor assembly;   d. detecting the absence of a stored verification template;   e. detecting the presence of a stored verification template that is partially complete;   f. detecting that power is being transmitted to the smart card for the first time;   g. detecting a specified instance of power being transmitted to the smart card;   h. detecting that a maximum number of unsuccessful attempts to derive a verification template has not been reached;   I. activating an input mechanism;   j. detecting that a timer or counter has not expired;   k. detecting the occurrence of an error state indicating that a recoverable error has occurred to prevent successful derivation or storing of a verification template;   l. detection of a flag set the last time the smart card was inserted in a card reader that transmits data to or from the smart card;   m. detecting that the smart card has been connected to a power source that does not transmit data to or from the smart card;   n. detection of a trigger event by a component of the smart card other than the biometric sensor assembly; and   o. detecting that a particular smart card has been coupled to a particular non-data-transmitting power source.       

     Embodiment 176 
     The system of any one of Embodiments 169 to 175, wherein the power element is a battery, a solar cell or a socket on the non-data-transmitting power source to allow connection to a mains power source. 
     Embodiment 177 
     The system of any one of Embodiments 169 to 176, wherein the biometric sensor assembly comprises a fingerprint sensor and wherein the receptacle comprises: 
     a card holder frame comprising one or more card guide rails into which the smart card is inserted to position the cardholder frame with respect to the smart card; and 
     a finger guide attached to the card holder frame and comprising two or more channels, wherein each channel is configured to position a finger placed thereon to contact the fingerprint sensor at a different orientation. 
     Embodiment 178 
     The system of Embodiment 177, wherein each channel is spaced from each other channel by an angle in a plane of a sensing surface of the fingerprint sensor. 
     Embodiment 179 
     The system of Embodiment 178, wherein at least one of the channels positions the finger to contact the fingerprint sensor at an elevation angle relative to the plane of the sensing surface. 
     Embodiment 180 
     The system of Embodiment 178 or Embodiment 179, wherein at least two channels position the finger to contact the fingerprint sensor at an elevation angle relative to the plane of the sensing surface and wherein the elevation angle of each of the two channels is different from the other. 
     Embodiment 181 
     The finger guide of any one of Embodiments 177 to 180, wherein each channel is spaced 90 degrees from one other channel. 
     Embodiment 182 
     A method for enrolling a biometric template on a smart card having a biometric sensor, the method comprising: 
     inserting an end of the smart card into a receptacle; 
     transmitting power to the smart card from the receptacle without transmitting data to or from the smart card; 
     causing the biometric sensor to operate in an enrollment mode; 
     while the biometric sensor is operating in enrollment mode, generating one or more biometric images with the biometric sensor; 
     deriving at least one verification template of biometric data from the one or more biometric images; 
     storing the verification template; and 
     after storing the verification template, terminating enrollment mode in the biometric sensor. 
     Embodiment 183 
     The method of Embodiment 182, comprising causing the biometric sensor to operate in the enrollment mode when power is transmitted to the biometric sensor assembly combined with the occurrence of a trigger event. 
     Embodiment 184 
     The method of Embodiment 183, wherein the trigger even comprises one or more trigger events selected from the group consisting of:
         a. user interactions with the biometric sensor assembly;   b. placing a detectable object on the biometric sensor assembly;   c. removing a detectable object from the biometric sensor assembly;   d. detecting the absence of a stored verification template;   e. detecting the presence of a stored verification template that is partially complete;   f. detecting that power is being transmitted to the smart card for the first time;   g. detecting a specified instance of power being transmitted to the smart card;   h. detecting that a maximum number of unsuccessful attempts to derive a verification template has not been reached;   I. activating an input mechanism;   j. detecting that a timer or counter has not expired;   k. detecting the occurrence of an error state indicating that a recoverable error has occurred to prevent successful derivation or storing of a verification template;   l. detection of a flag set the last time the smart card was inserted in a card reader that transmits data to or from the smart card;   m. detecting that the smart card has been connected to a power source that does not transmit data to or from the smart card;   n. detection of a trigger event by a component of the smart card other than the biometric sensor assembly; and   o. detecting that a particular smart card has been coupled to a particular non-data-transmitting power source.       

     Embodiment 185 
     The method of any one of Embodiments 182 to 184, further comprising automatically terminating enrollment mode in the biometric sensor upon terminating power transmission to the smart card. 
     Embodiment 186 
     The method of any of Embodiments 182 to 184, further comprising automatically terminating enrollment mode in the biometric sensor after the verification template of biometric data is stored. 
     Embodiment 187 
     The method of any one of Embodiments 182 to 186, further comprising providing a confirming indication that the biometric sensor is operating in enrollment mode. 
     Embodiment 188 
     The method of any one of Embodiments 182 to 187, further comprising illuminating a light or lights on the smart card confirming that the verification template is stored. 
     Embodiment 189 
     The method of any one of Embodiments 182 to 188, wherein the biometric sensor comprises a fingerprint sensor, and the verification template is derived from one or more fingerprint images. 
     Embodiment 190 
     The method of Embodiment 189, wherein generating one or more biometric images with the biometric sensor comprises instructing a user to contact the fingerprint sensor by placing the same finger on each of two or more finger guide channels configured to position the finger placed thereon in a different orientation with respect to the fingerprint sensor. 
     Embodiment 191 
     The method of Embodiment 189 or Embodiment 190, wherein deriving the least one verification template comprises determining that a specified number of acceptable fingerprint images has been generated. 
     Embodiment 192 
     A device to facilitate the enrollment of a verification template of fingerprint data in a fingerprint sensor-enabled smart card, the device comprising: 
     a receptacle configured to be removably coupled to the smart card; 
     a power element supported on the receptacle, wherein the receptacle is configured to transmit power from the power element to the fingerprint sensor of the smart card when the receptacle is coupled to the smart card; 
     a finger guide attached to the receptacle and comprising two or more finger guide channels, wherein the finger guide is configured so that each finger guide channel is adjacent the fingerprint sensor of the smart card when the receptacle is coupled to the smart card, and wherein each finger guide channel is configured to position a finger placed thereon to contact the fingerprint sensor at a different orientation; and 
     two or more status indicators, wherein each status indicator is associated with one finger guide channel and is configured to instruct the user with respect to the placement and removal of the user&#39;s finger with respect to the associated finger guide channel. 
     Embodiment 193 
     The device of embodiment 192, wherein the receptacle comprises one or more terminals configured to contact one or more corresponding power transmission contacts on the surface of the smart card when the receptacle is coupled to the smart card. 
     Embodiment 194 
     The device of embodiment 192 or embodiment 193, wherein the power element is a battery, a solar cell, or a socket connected to the receptacle to allow connection to a mains power source. 
     Embodiment 195 
     The device of any one of embodiments 192 to 194, wherein the receptacle comprises a card holder frame into which the smart card is inserted to couple the cardholder frame to the smart card. 
     Embodiment 196 
     The device of any one of embodiments 192 to 195, wherein each finger guide channel is spaced from each other finger guide channel by an angle in a plane of a sensing surface of the fingerprint sensor. 
     Embodiment 197 
     The device of any one of embodiments 192 to 196, wherein at least one of the finger guide channels positions the finger to contact the fingerprint sensor at an elevation angle relative to the plane of the sensing surface. 
     Embodiment 198 
     The device of any one of embodiments 192 to 197, wherein each finger guide channel is spaced 90 degrees from one other finger guide channel. 
     Embodiment 199 
     The device of any one of embodiments 192 to 198, wherein the status indicators comprise one or more of a light source, an audio source, a vibrating element, and a graphic display. 
     Embodiment 200 
     The device of any one of embodiments 192 to 199, wherein the status indicators comprise light sources disposed on the receptacle. 
     Embodiment 201 
     The device of any one of embodiments 192 to 200, wherein the status indicators comprise light sources disposed on the smart card that are visible at a surface of the receptacle when the receptacle is coupled to the smart card. 
     Embodiment 202 
     The device of embodiment 201, wherein the receptacle comprises graphic elements associating each of the light sources disposed on the smart card with at least one of the finger guide channels. 
     Embodiment 203 
     The device of embodiment 201, wherein the receptacle comprises light pipes configured to transmit light from each of the light sources disposed on the smart card to a surface location on the receptacle associated with at least one of the finger guide channels. 
     Embodiment 204 
     The device of embodiment 201, wherein the receptacle comprises a photo detect circuit configured to detect light from each of the light sources disposed on the smart card and to activate a status indicator on the receptacle that is associated with at least one of the finger guide channels. 
     Embodiment 205 
     The device of any one of embodiments 192 to 204, wherein the status indicators are powered by the power element when the receptacle is coupled to the smart card, and wherein the receptacle includes a switch configured to close a power circuit from the power element to the status indicators when the receptacle is coupled to the smart card and to open the power circuit from the power element to the status indicators when the receptacle is uncoupled from the smart card. 
     Embodiment 206 
     The device of any one of embodiments 192 to 205, further comprising a detector circuit configured to detect a signal from the smart card to activate the status indicators. 
     Embodiment 207 
     The device of any one of embodiments 192 to 206, wherein the receptacle comprises an injection molded plastic. 
     Embodiment 208 
     The device of any one of embodiments 192 to 197, wherein device is unable to transmit data between the device and any device other than the smart card. 
     Embodiment 209 
     A method for enrolling a fingerprint template on a smart card having a fingerprint sensor, the method comprising: 
     A. transmitting power to the smart card from a power source removably coupled to the smart card, the power source including a power element that provides power to the fingerprint sensor and a finger guide comprising two or more finger guide channels positioned adjacent to the fingerprint sensor of the smart card when the power source is coupled to the smart card, and wherein each finger guide channel is configured to position a finger placed thereon to contact the fingerprint sensor at a different orientation; and 
     B. during step A, instructing the user with respect to the placement and removal of the user&#39;s finger with respect to each finger guide channel with a status indicator associated with the finger guide channel. 
     Embodiment 210 
     The method of embodiment 209, wherein the status indicators comprise light sources disposed on the power source, and step B comprises selectively changing the light status of each light source to instruct the user to place the finger on or remove the finger from the associated finger guide channel. 
     Embodiment 211 
     The method of embodiment 209 or embodiment 210, wherein the status indicators comprise light sources disposed on the smart card which are visible to the user, and step B comprises providing graphic elements on a surface of the power source instructing the user to place the finger on or remove the finger from a finger guide channel based on an illumination status of the associated light source. 
     Embodiment 212 
     The method of any one of embodiments 209 to 211, wherein the status indicators comprise light sources disposed on the smart card, and step B comprises transmitting light from each of the light sources disposed on the smart card to a surface location on the power source associated with at least one of the finger guide channels. 
     Embodiment 213 
     The method of any one of embodiments 209 to 212, wherein the status indicators comprise light sources disposed on the smart card, and step B comprises detecting light from each of the light sources disposed on the smart card and activating a status indicator on the receptacle that is associated with at least one of the finger guide channels. 
     Embodiment 214 
     The method of any one of embodiments 209 to 213, further comprising, during step B: 
     generating two or more fingerprint images with the fingerprint sensor by instructing a user to contact the fingerprint sensor by placing the same finger on each of the two or more finger guide channels of the finger guide to position the finger placed thereon in a different orientation with respect to the fingerprint sensor; 
     deriving at least one verification template of fingerprint data from the two or more fingerprint images; and 
     storing the verification template. 
     Embodiment 215 
     The method of any one of embodiments 209 to 214, comprising causing the fingerprint sensor to operate in an enrollment mode when power is transmitted to the fingerprint sensor during step A combined with the occurrence of a trigger event. 
     Embodiment 216 
     The method of embodiment 215, wherein the trigger even comprises one or more trigger events selected from the group consisting of:
         a. user interactions with the fingerprint sensor;   b. placing a detectable object on the fingerprint sensor;   c. removing a detectable object from the fingerprint sensor;   d. detecting the absence of a stored verification template;   e. detecting the presence of a stored verification template that is partially complete;   f. detecting that power is being transmitted to the smart card for the first time;   g. detecting a specified instance of power being transmitted to the smart card;   h. detecting that a maximum number of unsuccessful attempts to derive a verification template has not been reached;   i. activating an input mechanism;   j. detecting that a timer or counter has not expired;   k. detecting the occurrence of an error state indicating that a recoverable error has occurred to prevent successful derivation or storing of a verification template;   l. detection of a flag set the last time the smart card was inserted in a card reader that transmits data to or from the smart card;   m. detecting that the smart card has been connected to a power source that does not transmit data to or from the smart card;   n. detection of a trigger event by a component of the smart card other than the fingerprint sensor; and   o. detecting that a particular smart card has been coupled to a particular device.       

     Embodiment 217 
     The method of embodiment 215, further comprising automatically terminating enrollment mode in the fingerprint sensor upon terminating power transmission to the smart card. 
     Embodiment 218 
     The method of embodiment 215, further comprising providing a confirming indication that the fingerprint sensor is operating in enrollment mode. 
     Embodiment 219 
     The method of embodiment 214, further comprising activating one or more status indicators confirming that the verification template is stored. 
     Embodiment 220 
     The method of any one of embodiments 209 to 219, wherein during step B, the status indicators are selectively changed in a sequence that includes all of the finger guide channels, moving from one finger guide channel to another after an acceptable image has been gathered at the previous finger guide channel. 
     While the subject matter of this disclosure has been described and shown in considerable detail with reference to certain illustrative embodiments, including various combinations and sub-combinations of features, those skilled in the art will readily appreciate other embodiments and variations and modifications thereof as encompassed within the scope of the present disclosure. Moreover, the descriptions of such embodiments, combinations, and sub-combinations is not intended to convey that the claimed subject matter requires features or combinations of features other than those expressly recited in the claims. Accordingly, the scope of this disclosure is intended to include all modifications and variations encompassed within the spirit and scope of the following appended claims.