Abstract:
A tracking device is provided. A position determiner is configured to determine a position of the tracking device. The tracking device has first and second operating modes, the first operating mode being in response to at least the absence of a data communications link with an external wireless node, the second operating mode being in response to at least the presence of communication with an external wireless node. In the first operating mode, the tracking device periodically determines its position from the position determiner and maintains a position history of the tracking device. In the second operating mode, the tracking device reduces the operations of the position determiner relative to the first operating mode. In association with the tracking device transitioning from the first operating mode to the second operating mode, the tracking device wirelessly transmits the position history.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 11/847,146, filed Aug. 29, 2007, which claims priority of U.S. Provisional Patent Application Ser. No. 60/840,844, filed Aug. 29, 2006, and U.S. Provisional Patent Application Ser. No. 60/859,232, filed Nov. 15, 2006, the entire contents of which are incorporated herein by reference. This application is also related to U.S. patent application Ser. No. 11/847,106 entitled “Active Wireless Tag and Auxiliary Device for Use With Monitoring Center for Tracking Individuals or Objects.” 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to systems which provide location tracking and monitoring of a portable tracking device or “tag” that is affixed to an individual or other object, and in which the device periodically communicates data to a remote monitoring station. More specifically, the present invention relates to the implementation of limited RF capability in the tag and another system device, hereinafter “auxiliary device” to provide improved system features and functions. 
     BACKGROUND OF THE INVENTION 
     Electronic location monitoring and tracking of individuals or objects can be carried out in a number of ways. Determining the location of the tag can be provided using well-known techniques, such as GPS, cellular triangulation, or a combination of both. Further, in certain system applications, tamper detection capability and the ability to generate alarms upon detecting tampering or upon other conditions may be included. There are variants of electronic location monitoring and tracking systems. For example, some systems rely upon electronic monitoring at a fixed located such as the individual&#39;s home or place of employment. These systems can rely upon a land line telephone link and are commonly known as house arrest systems. These systems utilize a transmitter worn by the individual and a stationary receiver located at the monitoring location. When the individual is an “offender”, i.e., a person under a government-supervised program, the transmitter incorporates tamper-detection capabilities and upon such detection may transmit an alarm. The worn transmitter transmits a signal a short distance to the receiver located at the monitoring location. The receiver communicates with a central monitoring service over standard telephone lines. The tracking system of this type is limited in that it can only provide an indication of the presence or absence of the individual at the monitored location at a given time. This type of system cannot offer location information if the individual leaves the monitored location. 
     U.S. Pat. Nos. 5,867,103 and 6,160,481, which are incorporated by reference herein, disclose a system which provides for a locational tracking of a plurality of monitored persons. The system has a portable monitoring device for each of the monitored persons. Each portable monitoring device has means to secure the device to a respective monitored person and may include means to detect tampering with the secured device for offender applications. Additionally, each portable monitoring device has means to receive a distinct signal generated by a detached sending unit. Each portable monitoring device also has means to transmit a signal containing data. The system further has means to acquire the signal containing data transmitted by each respective portable monitoring device. The system has means to determine a positional location of the portable monitoring device based, at least in part, upon the distinct signal received by the portable monitoring device. The system has means to mark, at least within a range of time references, when the positional location reference was determined in the form of an occurrence reference. The system has means to store, for archival retention within a locational tracking database, at least a series of the position references and associative occurrence references of each portable monitoring devices of the tracking system. 
     U.S. Pat. No. 6,774,797, which is incorporated by reference herein, discloses a one-piece lightweight waterproof personal tracking tag which is attached to an individual using either a tamper detection strap or other suitable means of connection. The tag communicates with a global positioning satellite network and a wireless network to obtain geographic location information and to exchange data with a centralized data system. The tag monitors the location of the wearer of the tag, compares the monitored location to a database of acceptable and unacceptable location and time parameters and provides updates to a centralized database system, the monitoring station, and receives downloads and updates from the system. 
     For locational tracking and monitoring of one or more individuals, each having an individual set of allowed geographic and temporal restrictions, the system must maintain an extensive database of individuals and corresponding restrictions. In such applications, the tag preferably incorporates a microcontroller, flash memory, a cellular modem, a GPS receiver, tamper detection, and a rechargeable battery in a single lightweight unit. One or more individuals are provided with a tracking tag. Each of the tags reports into the monitoring station on a periodic basis. The reporting basis can be on a predetermined schedule and/or can be based upon detection of a violation or other reportable condition detected by the tag itself. Information reporting by the various tags is recorded and analyzed at the monitoring station by the data tracking system to determine if individual violations have occurred. The centralized data tracking system can then take an appropriate action to notify, respond to and/or correct the noted violation. 
     The tag&#39;s ability to properly function is limited by the capabilities of the tag&#39;s battery and the ability of the tag&#39;s circuitry to function properly in different locations. Current GPS based tracking systems, for example, will not function properly when GPS reception becomes impaired or is lost. In addition, the demands of system applications place increasing power loads and operating time requirements on the tag&#39;s batteries. Both of these shortcomings can be especially acute in offender tracking and monitoring applications where loss of offender locational monitoring is unacceptable. It would be desirable to provide a mechanism for efficiently extending the range of such GPS tracking systems particularly in areas in which GPS reception is impaired. It would also be desirable to provide such extended coverage where no action is required by the offender. It would also be desirable to provide such expanded coverage where removal of the offender&#39;s GPS device is not required. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a wireless location tracking device or tag and auxiliary device for use with a home monitoring unit for tracking individuals or objects. The location tracking device has position determining circuitry and first short range wireless circuitry that communicates position data representative of the location of the tracking device to an auxiliary device. The auxiliary device has second short range wireless circuitry that communicates with the tracking device and long range communications circuitry that communicates the position data to a remote location. The tracking device can have a first operational mode, when communication is not established with the auxiliary device, wherein the position determining circuitry is maintained in a normal power state. The tracking device can also have a second operational mode, when communication is established between the tracking device and the auxiliary device, wherein the position determining circuitry is placed in a reduced power state. 
     The remote location can include a monitoring station that communicates with the tracking device via the auxiliary device. The monitoring station can direct the tracking device to switch operational modes. In the alternative (e.g., in cases where the tag is unable to contact the CMS) the tag can maintain list of approved auxiliary devices and the tag can make the determination on whether or not switch operational modes. This list of approved auxiliary devices can be updated by the CMS as needed. The auxiliary device can be configured as a home monitoring unit having a housing and tamper detection circuitry that detects unauthorized movement or opening of the auxiliary device. The tracking device can optionally communicate with the home monitoring unit and a passive auxiliary device having third short range wireless circuitry, thereby extending the range of the home monitoring unit. 
     The tracking device can include signal strength circuitry associated with the first short range wireless circuitry so that the tracking device can determine whether radio energy received by the first short range wireless circuitry is below a predetermined threshold. In the alternative, the auxiliary device can include signal strength circuitry associated with the first short range wireless circuitry so that the tracking device can determine whether radio energy received by the first short range wireless circuitry is below a predetermined threshold. 
     The tracking device and/or the auxiliary device can includes time slot allocation circuitry or frequency allocation circuitry allowing the tracking device or auxiliary device to minimizes contention for frequencies or time slots associated with the short range wireless circuitry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, reference is made to the following description and accompanying drawings: 
         FIG. 1  shows a block diagram of a system in accordance with the invention; 
         FIG. 2  is a block diagram of a tracking tag in accordance with the invention; 
         FIG. 3  shows a block diagram of an auxiliary device in accordance with the invention; 
         FIG. 4  shows a block diagram of an exemplary HMU range expansion scenario in accordance with the invention; and 
         FIG. 5  shows a block diagram of an exemplary one-piece passive tracking tag scenario in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a block diagram of a system in accordance with the invention. The system includes a central monitoring system (CMS)  10 , a tracking tag  20  operable to communicate with a Global Positioning Satellite (GPS) network  30  and one or more auxiliary devices  40 . The strap or tag may incorporate tamper detection using a variety of well-know technologies. The tag  20  can be attached to an object or individual using a strap or other suitable means of connection. For example, the tag can be attached to a package that is being transported from one location to another. In the alternative, the tag can be attached to in individual under “house arrest” that being monitored for compliance. Numerous other scenarios can be envisioned without departing from the scope of the invention. 
     The tag  20  communicates with the GPS network  30  and a Home Monitoring Unit (HMU)  300  to respectively obtain geographic location information and to exchange data with the CMS  10 . The CMS monitors the location of the tag (as well as the object or individual to which the tag is attached) and compares the monitored location to a database of acceptable and unacceptable location and time parameters. The tag generally transmits position data updates, via the HMU, to the CMS and also receives downloads and updates from the CMS via the HMU. 
     In order to track one or more individuals or objects, each of which having an individual set of allowed geographic and temporal restrictions, the CMS  10  maintains a database  15  of individuals or objects and corresponding restrictions. In one embodiment, the tag  20  generally incorporates a microcontroller, flash memory, an RF transceiver, a GPS receiver, tamper detection, and a rechargeable battery into a single unit as discussed in more detail below. While the foregoing description focuses primarily on tracking of individuals, it is understood that the invention is equally applicable to the tracking of objects as well. 
     In system applications where the location of a plurality of individuals are being monitored and tracked, each such individual is provided with a tracking tag. To lengthen battery life and reduce data accumulation, each of the tags preferably reports into the CMS  10  on an intermittent or periodic basis. The reporting basis can be on a predetermined schedule and/or can be based upon detection of a violation or other reportable condition detected by the tag itself. Information reporting by the various tags is recorded and analyzed at the CMS to determine if individual violations have occurred. The CMS can then take an appropriate action to notify, respond to and/or correct the noted violation. 
     The system can also include one or more auxiliary device  40 . The auxiliary device  40  works in conjunction with the tag  20  which will intermittently or periodically request the presence of an auxiliary device  40  by sending out a RF transmission (“ping”) and waiting for a reply from any auxiliary device in range via the short range radio (or RF) link  45 . The typical range in an exemplary system is approximately 100 meters in open area. The auxiliary device includes: power supply circuitry (e.g., for AC or DC power), battery charging circuitry, a battery backup for remote operations, a RF transceiver, a microcontroller and various alarm features to detect and report movement, power loss and light ingress as discussed in more detail below. Each auxiliary device can be identified by a unique serial number which is transmitted in its response to a ping from tag  20 . The auxiliary device serial number can also be transmitted in a last reported alarm status response. The auxiliary device  40  can store any alarms in non volatile memory to ensure that in the event of loss of power data is retained. The auxiliary device can also retain the status of any alarms until it is able to reply to a valid request from tag  20 . 
     I—Tracking Tag 
       FIG. 2  is a block diagram of a tag  20  in accordance with the invention. The tag  20  has a microcontroller  102 , associated flash memory  104  and a GPS receiver  106  which provides up GPS position information to the microcontroller  102 . Active tags can include a cellular modem with an associated SIM card provided for data communication between the tag  20  and the CMS  10 . However,  FIG. 1  shows a “passive” tag  20  that communicates through a short range RF link  45  and HMU  300  in order to communicate with the CMS  10 . This configuration is particularly useful in house arrest or work release scenarios. The tag  20  also communicates with one or more GPS satellites in the GPS network  30 . The tag  20  also includes an RF transceiver  150  for communication between the tag and the auxiliary device  40  via the RF link  45 . This RF link creates an electronic tether between the tag and the auxiliary device. Suitable short range wireless integrated circuits and networking firmware for use in accordance with the invention are available from a variety of sources including Micrel Inc., of San Jose, Calif. (www.micrel.com). In the embodiment discussed below, the tag communicates with the monitoring station via the RF link and a cellular modem is not used. As noted above, a tag that communicates with the CMS via an RF link (without the benefit of a cellular modem) is referred to herein as a “passive” tag. Communication via the RF link  45  is discussed in more detail in the following section. 
     The tag can obtain position data through the GPS network  30 . The CMS can also determine the location of the tag based on the known position of an auxiliary device or HMU. The tag also includes a battery  112  to power the microcontroller  102 , the GPS receiver  106  and the other components within the tag  20 . The battery  112  resides within the unit in a sealed compartment and is not removed for recharging so as to avoid potential leaks which could result from removal and replacement of the battery. Because the unit must be worn by an individual at all times, the tag will be subjected to water in such environments as showering. The battery  112  is recharged while it remains within the tag  20  by means of charger  113 . 
     The tag may also include a tamper detection mechanism  114  to avoid unauthorized removal or opening of the tag. The specific tamper detection mechanism can be implemented in a variety of ways including: i) signal continuity detection, ii) electrical, optical or electromagnet switches or detectors that detect unauthorized opening of the tag and/or iii) electrical, thermal proximity devices which monitor the proximity of the tag to the individual or object. Accelerometer  115  is also provided and can be used to monitor acceleration of the tag  20 . The microcontroller  102  can be programmed to generate an alarm based on acceleration beyond a threshold or the like. 
     The microcontroller  102  controls the operation of the tag  20 . Regular polls of the GPS receiver  106  and RF transceiver  150  are carried out to monitor for incoming command messages and to monitoring the location of the tag. The parameters of the monitoring to be performed are programmed into the microcontroller  102  to respond to variations in the location of the tag and to respond to commands received from the CMS  10  through the HMU  300 . 
     The flash memory  104  holds the programmed code for the operation of the tag  20 . The code is downloaded to the unit utilizing a serial link and can be modified and/or downloaded through the HMU  300 . In the alternative, the code can be downloaded via programming port  124 . 
     Communication between the tag  20  and the CMS  10  is carried out via the HMU  300 . The tag can also be polled by the CMS to download the position of the tag as measured by the GPS system and/or to download other operating parameters such as violation history, position history and/or battery status. 
     The microcontroller  102  is programmed to monitor for alarm conditions, such as violations of restrictions by the tag wearer. In the event that an alarm condition occurs, for example low battery voltage, a tamper detection by the tamper prevention unit  114  or a violation of the geographic limitations set for the wearer of the tag, the microcontroller communicates an alarm condition to the CMS  10 . The microcontroller can run continuously or can be programmed to cycle the entire tag through an intermittent power pattern, such as a sleep mode, to conserve battery power. 
     The microcontroller code also includes the ability to be manually placed into a sleep mode wherein the unit is not powered down but only inactive, upon receipt of an appropriate command from the CMS  10 . Powering down of the tag  20  can be used to prolong the life of the battery  112 . By allowing a power down to be controlled by the CMS, the tag can be powered down without the knowledge of the offender. Because the individual does not know when the unit is inactive, the individual cannot take advantage of inactivity to commit an offense without detection. The unit can reactivate after a set period of time, after being connected to a recharger or after receipt of a command to reactivate. 
     The GPS module is used with an appropriate antenna  116 , such as a patch antenna mounted internal to the tag case. The GPS module can also include a battery backup  130  to minimize the drain on the main battery  112 . The GPS module when activated will obtain the current position of the tag. If no fix is obtained, the tag will report that no fix was obtained. To minimize the power consumption and therefore maximize the battery charge life, the GPS receiver is used in the push to fix mode. The receiver is normally asleep and, only when requested, wakes to obtain the current position of the tag. 
     The tag  20  can include an audible alarm such as a buzzer  118 , a tactile alarm such as a vibrator  120  to provide an indication to the wearer that a condition requiring attention has been detected. The tag can also include a panic button  122  to allow the wearer to alert the CMS  10  that a situation requiring attention exists. This button can be particularly useful when the tag is used by an individual being monitored because of the individuals potential need for assistance. Other visual alerts such as Tricolor LED  126  (e.g., for system status and the like) and Tamper LED  128  can be provided. 
     II—Auxiliary Device 
       FIG. 3  shows a block diagram of an auxiliary device  40  in accordance with the invention. A “passive” auxiliary device  40  has a microcontroller  202  with associated internal memory and an RF transceiver  250  for communication between the tag  20  and the auxiliary device  40  via the RF link  45 . It is understood that the microcontroller  202  can utilize internal memory, external memory or both. The auxiliary device also includes a battery  212  to power the microcontroller  202 , RF transceiver  250  and the other components within the auxiliary device. The battery  212  is recharged by means of charger  213 . The programming code for microcontroller  202  can be downloaded via typical techniques. For example, the programming for microcontroller  202  can be burned into the appropriate memory device prior to or during assembly. In the alternative, programming code can be downloaded via optional programming port  224 . 
     The auxiliary device can optionally include a tamper detection mechanism  214  to avoid unauthorized removal or opening of the auxiliary device. An accelerometer  215  can optionally be provided and can be used to monitor movement of the auxiliary device. The microcontroller  202  can be programmed to generate an alarm based on acceleration beyond a threshold or the like. The auxiliary device  40  may also include an audible alarm such as a buzzer  218  to provide an indication that a condition requiring attention has been detected. The auxiliary device is preferable constructed with a small housing (e.g., 120 mm*80 mm*55 mm) and can be attached to AC power via a suitable cable or adapter (e.g., 12V adapter). The auxiliary device can be designed to be hard mounted via screws or other suitable fasteners. In the alternative the auxiliary device can be temporarily placed in a location or even worn or carried by an individual (e.g., operating via battery power). For example, the auxiliary device can be integrated into or attached to an article of clothing such as shoes, socks, pants, shirts, or jackets. In the alternative, the auxiliary device can be integrated into or attached to a backpack, purse, wallet or other convenient portable accessory. 
     In operation, the tag  20  will periodically poll (e.g., ping) for the presence of an auxiliary device  40  via the RF link  45 . If an auxiliary device is detected (i.e., the auxiliary device responds to the ping) and communications can be established with the auxiliary device, the operational parameters of the tag and/or the system can be altered. The auxiliary device  40  will typically reply to a tag  20  with some or all of the following information: auxiliary device ID, tag ID, Status of the tag (tamper, low battery and charging), status of the auxiliary device (tamper, motion or power). This information is then transmitted to the CMS  10  via the HMU. It understood that a variety of communications protocols are suitable for use in accordance with the invention. It is also understood that in some embodiments, communications between the tag and the auxiliary device can be initiated by the auxiliary device. 
     Several modes of operation are discussed in detail below. In each of these examples, the tag  20  relays messages though an auxiliary device or HMU to the CMS via a short range RF link. This configuration is advantageous in that the tag and the auxiliary device do not require a cellular modem to communicate to the CMS. This results in considerable cost savings and minimizes power utilization. It is understood that the auxiliary device may optionally include other communication and processing capabilities so that it can function as an HMU. In this case the auxiliary device is considered “active” and includes optional communications capabilities or communications hardware  252  can include one or more of the following: a modem, cellular modem, network connection, wireless communications device or the like to facilitate communication with the CMS. 
     III—Inclusion Zone Operation (GPS Power Down) 
     In this mode of operation, the location of the auxiliary device  40  or HMU  300  is fixed and is known to the CMS  10  (e.g., the location of the auxiliary device is stored in the CMS database  15 ). The system is operable to establish an inclusion zone defined by the range of the auxiliary device. In this mode, so long as the tag  20  is in communication with the auxiliary device or HMU, the CMS knows the location of the tag  20 . Operation in this mode proceeds as follows: the tag  20  detects an auxiliary device or HMU (i.e., the auxiliary device or HMU responds to a ping). The tag establishes communications with the auxiliary device or HMU, and reports some or all of the following information to the CMS  10 : location information, auxiliary device ID, tag ID, Status of the tag (tamper, low battery and charging), status of the auxiliary device (tamper, motion or power). The auxiliary device can also be configured to recognize one or more auxiliary device groups (e.g.,  40 ,  40 ′,  40 ″,  40 ′″) and then alter its operating mode subject to a receipt from the auxiliary device that it has no alarms pending. 
     As an additional precaution, software in the tag  20  or the CMS may require a valid GPS fix before entering a low power mode. The tag  20  will contact the CMS  10  to confirm it is going to sleep (i.e., GPS receiver  106  can be powered down in order to save battery power). In cases where the tag is unable to contact the CMS, the tag can maintain list of approved auxiliary devices and the tag can make the determination on whether or not to enter a reduced power state. This list of approved auxiliary devices can be updated by the CMS as needed. This mode is particularly advantageous in locations where GPS reception is impaired. 
     In some cases, the individual to which the tag is attached may be permitted to travel outside the range of the HMU or an auxiliary device (e.g., to travel to work or another acceptable location). If the tag  20  cannot calculate its position via GPS, contact the CMS  10  or if the tag receives an alarm status from the auxiliary device  40 , it will remain in normal operating mode and will continue to log its status. The logged information can then be transmitted to the CMS once communication is established between the tag and the HMU or auxiliary device. It is understood that the location of the auxiliary device  40  can be fixed after the auxiliary device is powered up in a given location. Upon the initial communication between the tag and the CMS, the system can enter the location of the auxiliary device  40  into the database  15  before allowing the tag to enter a low power mode. 
     During low power mode, the tag  20  will continue to check for tampers on both itself and the auxiliary device  40 . Also during low power mode, the tag  20  can increase its ping rate to the auxiliary device  40  to ensure it remains in range. The ping rate can be set to a random period between two time ranges to minimize contention with other RF devices. The tag  20  can receive a response from any member of its associated auxiliary device group and will remain asleep. During this mode, the tag  20  can also be configured to wake up at pre-set intervals to refresh its GPS position and therefore update its empheris and almanac from any GPS satellites in view. This ensures that when the tag  20  finally leaves range of an auxiliary device  40 , it is able to quickly obtain a GPS position. The tag  20  can also be configured to contact the CMS  10  at this point and report its status without the need to obtain a new GPS position before going back to low power mode. 
     Upon an alarm condition (e.g., power loss, movement or tamper, lack of valid pings . . . ) the tag  20  will wake up and resume normal mode. The tag  20  will immediately contact the CMS  10  and report its status. 
     IV—HMU Range Expansion 
     One or more auxiliary devices can also be used to extend the range of a Home Monitoring Unit (HMU) when used in a traditional “house arrest” situation. This is shown graphically in  FIG. 4 . In general, the HMU  300  communicates with the CMS  10  via long range communication link  302  (typically a land line telephone link to the PSTN). It is understood that communications link  302  can utilize a modem, cellular modem, a network connection, wireless communications device or other hardware that can facilitate long range communications. In this scenario, the HMU is also provided with an RF receiver that is operable to monitor the RF link (or electronic tether) established between a tag  20  and an auxiliary device  40 . Each auxiliary device  40  can be positioned such that it can receive information from a tag  20  via the RF link  45 . The auxiliary device  40  is also positioned in range of the HMU. This allows the HMU receiver to receive the reply message (from the auxiliary device to the tag) even when the tag is out of range. Receipt of the reply from the auxiliary device in effect allows the HMU to determine that the tag is within an acceptable range. The auxiliary device will only be treated as a valid source if it is previously assigned to the HMU and is not in a current alarm status. 
     V—RF Network Contention—RF Frequency Allocation 
     In the scenarios discussed above, the RF link  45  is utilized for communication between various devices. In certain scenarios, several devices may be utilized in relatively close proximity. These devices may ultimately be in contention for use of the RF link. That is two or more devices may try to communicate via the RF link simultaneously. Accordingly, the RF link can be implemented to eliminate or reduce contention issues. For example, the RF link can be implemented with a plurality of frequencies that are allocated to various devices. In another example, the RF link can be implemented with a time slot allocation for each device. Such time slots can be assigned on a fixed or dynamic basis. 
     In the example shown in Table 1 below, the RF link  45  is implemented with four frequencies. 
     
       
         
               
               
               
             
           
               
                   
               
               
                 Frequency No. 
                 Associated Device 
                 Description 
               
               
                   
               
             
             
               
                 1 
                 HMU 
                 Dynamic Time Slot 
               
               
                   
                   
                 Allocation 
               
               
                 2 
                 Auxiliary Device 
                 Frequency Allocation 
               
               
                 3 
                 Auxiliary Device 
                 Frequency Allocation 
               
               
                 4 
                 Auxiliary Device 
                 Frequency Allocation 
               
               
                   
               
             
          
         
       
     
     In this example, frequency number 1 is utilized for communication between a tag and an HMU. The frequency band is divided into a plurality of time slots, each of which can be assigned to a specific tag. Time slot allocation can be performed on a fixed or dynamic basis. In the case of fixed time slot allocation, the given time slot can be directly programmed into the specific tag as well as the associated HMU prior to any communication taking place. In the case of dynamic time slot allocation, the tag and HMU can conduct initial communications (e.g., utilizing a pre-selected time slot) before a specific time slot is assigned to a specific tag. 
     In this example, frequencies 2-4 are generally utilized by a tag to communicate with an auxiliary device. In normal operation tag will intermittently or periodically request the presence of an auxiliary device by sending out a RF transmission (“ping”) and waiting for a reply from any auxiliary device in range via the RF link. Each ping can be transmitted on a different frequency (2-4) until communication between the tag and the auxiliary device is established. Specific frequency can be selected on specific pattern or random frequency assignment. 
     VI—Wireless Link—Range Adjustment 
     In certain scenarios, it may be desirable to adjust the range of the wireless (RF) link  45 . For example, the default communication range between a tag  20  and an auxiliary device  40  or HMU  300 ,  300 ′ may extend into unintended areas such as adjoining property. Accordingly, the receiver in the auxiliary device  40  or HMU  300 ,  300 ′ may include the capability to provide Received Signal Strength Indication measurements (RSSI). 
     It is generally understood that RSSI measurements denote the received radio signal strength. These measurements can be utilized in connection with a variety of system functions. For example, RSSI can be used internally in a wireless networking card to determine when the amount of radio energy in the channel is below a certain threshold at which point the network card is clear to send (CTS). RSSI can be measured in the IF stage before the IF amplifier. In zero-IF systems, it can be done in the baseband signal chain, before the baseband amplifier. RSSI measurements can be output as a DC analog level. However, it is beneficial to sample RSSI measurements with an internal A/D converter so that resulting numeric codes available directly to the internal processor  202  ( FIG. 3 ). In the example below, typical RSSI measurements range from about 250 (noise level) to about 650 maximum. 
     In the context herein, RSSI is utilized to determine the relative proximity or range of the tag  20  to an auxiliary device  40  or HMU  300 ,  300 ′. This can be accomplished by selecting a predetermined RSSI value to set the acceptable range of the RF link  45  (i.e., the RSSI must remain above the pre-determined RSSI level to be considered within range). In the alternative, a calibration routine can be utilized. For example, the tag can be placed into a range calibration mode in which it pings every few seconds. The tag can then be moved throughout the desired location during which the auxiliary device  40  or HMU  300 ,  300 ′ records the lowest RSSI measurement. Once the tag has been moved throughout the entire location at issue, the calibration process is complete and the lowest RSSI measured from the calibration process is used to set the range of the RF link  45 . The system can optionally include an acceptable offset range for the RSSI measurement (e.g., user selectable) to account for environmental conditions. In this example, a typical default level for the offset range is 50. It is understood that a variety of antenna types (e.g., omnidirectional, directional . . . ) having various characteristics (gain, impedance, directionality, radiation efficiency and the like) can be utilized in combination with the RSSI based range adjustment discussed above to provide optimal coverage in a given scenario. 
     X—Suggested Uses of Each Mode 
     1) Inclusion Zone Operation (GPS Power Down)
         To confirm the known location of an individual to the vicinity of an auxiliary device or auxiliary device when GPS is unavailable i.e. at home or in a establishment i.e., hostel.   To extend the operational life of the tag battery by allowing the tag to use the auxiliary device in a known location.       

     2) HMU Range Expansion
         To allow the auxiliary device to be positioned in such a way that with the operation of the HMU, a property can be effectively covered with the placement of auxiliary device to extend the HMU range.   The auxiliary device can be used in a number of modes depending on parameter settings on the tag and if a Home Monitoring unit (HMU is present).       

     While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be understood that various changes and modifications may be made without departing from the scope of the present invention.