Abstract:
A customer conversion system connects existing, conventional sensors to a point of sale computer or other computer. Entries by people into a retail space so equipped are counted and recorded on a continuous or on a periodic interval basis.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to methods and apparatus, which perform customer counting in the retail environment. 
     2. Related Art 
     Several technologies exist for counting customers in the retail environment. One objective of such systems is to determine the customer conversion rate in a particular environment. Customer conversion rate is the ratio of the number of customers who enter the environment, i.e., the amount of traffic in a location, to the number of sales or to the dollar value of the sales in the particular environment. Computing customer conversion ratios in a quick and accurate fashion is important to retailers desiring to evaluate and improve their retail environments. 
     In order to compute customer conversion ratios, information must be obtained from two, usually independent, sources. Customer counts must be obtained from some sort of manual or automatic, direct or indirect observation of traffic. Numbers or values of sales must be obtained, usually from point of sale computers or terminals, or central sales logging computers, or the like. 
     One method of counting customers is to observe a retail environment with video equipment. The images obtained therefrom can be processed to determine the number of customers who move through an area in a given period of time. Such systems are complex and require expensive installation by skilled technicians for proper operation. 
     Another method of counting customers is to incorporate a tag device into an article like a shopping cart, which is then detected when the customer moves the cart past a suitable sensor. Again, the system and tagged carts are expensive and require installation by skilled technicians for proper operation. 
     Yet another method of counting customers involves deploying sensors in locations to be monitored. McGregor et al. disclose such a system in U.S. Pat. No. 5,250,941-B1. Simple sensors, such as pressure sensitive strips, carpeting and the like, ultrasonic, infrared, and other presence or movement detectors can be used. A principle disadvantage of such deployments of sensors is simply the expense and inconvenience of having to install and maintain them throughout the areas to be monitored. Another disadvantage is that such sensors can be fooled into undercounting or overcounting traffic depending on the exact pattern of traffic and sensor characteristics. 
     SUMMARY OF THE INVENTION 
     It is a general object of the invention to provide an improved customer counting system in a retail environment. 
     According to one aspect of the invention, there is a customer conversion system, comprising a data processing unit including a real-time clock and an input, a sensor having an output indicative of each activation of the sensor, and an interface unit connecting the output of the sensor to the input of the data processing unit. In one variation, this system may include a security system to which the sensor output is connected. In another variation, the system may include a software program executing on the data processing unit which performs receiving the output of the sensor from the interface unit, and storing a record of the output of the sensor together with a time-stamp based on the real-time clock. In yet another variation, the system may include another sensor having an output indicative of each activation of the other sensor, another interface unit connecting the output of the other sensor to the input of the data processing unit, and a multiplexer through which the interface unit and the other interface unit connect the output of the sensor and the output of the other sensor to the input of the data processing unit. 
     According to another aspect of the invention, in a retail store including a security system having sensors which detect entry of a person and a point of sale computer including a real-time clock, a customer conversion system may include an interface unit connecting the sensor from the security system to the point of sale computer, and a software program executing on the point of sale computer which receives a signal indicating entry of a person from the sensor through the interface unit, and stores a record of receipt of the signal together with a time-stamp indicating when the signal was received. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, in which like reference designations indicate like elements: 
     FIG. 1 is a block diagram illustrating an embodiment of one aspect of the invention; 
     FIG. 2 is a block diagram illustrating an embodiment of another aspect of the invention including a multiplexer; 
     FIG. 3 is a block diagram illustrating an embodiment of the invention integrated with a security system; 
     FIG. 4 is a block diagram illustrating an embodiment of another aspect of the invention including a multiplexer and integrated with a security system; 
     FIG. 5 is a block diagram illustrating a CCS Sensor Interface unit of the embodiments of FIGS. 1-4; and 
     FIG. 6 is a block diagram illustrating a CCS multiplexer of the embodiments of FIGS.  2  and  4 . 
    
    
     DETAILED DESCRIPTION 
     The present invention will be better understood upon reading the following detailed description of a number of embodiments and aspects thereof, in conjunction with the drawings. 
     The invention is illustrated herein by the description of several embodiments thereof in Customer Conversion Systems (CCSs). One exemplary CCS is a system comprised of a combination including off the shelf components and new components illustrated by the block diagram of FIG. 1, described below. A CCS system  100  may include: 
     a Point of Sale (POS) computer or other computer  101  including a real-time clock (RTC); 
     a CCS Sensor Interface Unit  102 ; and 
     one or more activity sensors  103 . 
     The CCS Sensor Interface Unit  102  may require its own power supply  104 , as well. 
     The exemplary system counts customers at a lower cost than other, currently available methods. Lower cost in the exemplary system is accomplished in part through a low cost interface to existing or inexpensive conventional sensors  103 , such as existing or conventional door alarm sensors, and in part through simple installation. The cost of the CCS Sensor Interface Unit  102  is kept low by using a single chip microcontroller and excluding a real time clock. The exemplary system  100  takes advantage of the real time clock that is already in the POS computer or other computer  101 . The installation is made simpler and quicker by using intelligent modes in the CCS Sensor Interface Unit  102 , making it compatible with a variety of conventional activity sensors  103 , and displaying status in a simple, intuitive manner. Moreover, because the size and shape of the point of entry to be monitored by the sensors  103  is generally controlled to create predetermined traffic patterns, the sensors  103  and point of entry design can be combined to limit the degree of over- or undercounting reported by reliably producing a sensor output for each customer. 
     As will be understood upon reading the following description, a fairly low-level security system technician can easily install the CCS Sensor Interface Unit  102  successfully without access to the computer  101 . If required, more skilled personnel can finish the job later. 
     According to another advantageous aspect, the exemplary system is modular. CCS Sensor Interface Units  102  can be produced at low cost in high volumes. A number of CCS Sensor Interface Units  102  can be multiplexed together when more inputs are required than available in a single unit. A multiplexed system  200 , as shown in FIG. 2, may include at least the following: 
     a Point of Sale (POS) computer or other computer  101 ; 
     a CCS Multiplexer  201   
     2 or more CCS Sensor Interface Units  102 ; and 
     multiple activity sensors  103 . 
     Also, as explained below, the CCS Sensor Interface Unit  102  can be connected in parallel with sensors that are already attached to an existing store security system. 
     In order to render the following discussion clear, a number of definitions are now given with reference to FIGS. 1 and 2. 
     Point of Sale (POS) Computer or other Computer  101 —This is a computer that monitors a communications medium  105  connecting the POS computer or other computer  101  to the CCS Sensor Interface Unit  102 , or a medium  202  connecting the computer  101  to a CCS Multiplexer Unit  201 , and records sensor  103  activations during specific time intervals (e.g., 10, 15, 30 and 60 minute intervals). The POS computer may be a computer with the Microsoft Windows operating system, but any computer could be used. Although the following examples refer to a POS computer  101 , it will be understood by the skilled artisan that another computer with a real-time clock could also be used. 
     CCS Sensor Interface Unit  102 —This is a specially designed unit that monitors changes in sensors  103  (e.g., switch closure, relay closure or solid state semiconductor signal). This device has a circuit or switch whose position or state defines the sensor  103  polarity (i.e. whether the switch is either normally open or normally closed). This device  102  has indicators that communicate to a person whether the device  102  is working properly or not. This device  102  includes a connection to the communication medium  105  through which a sensor event may be communicated to a computer or a connection to a medium  203  through which a sensor event may be communicated to a computer through a multiplexing device, such as CSS Multiplexer Unit  201  described below. 
     Human Motion Sensor  103 —This part of the system  100  or  200  consists of any type of sensor that can be activated by a human and has a switch contact or solid state output. These will typically be door switches or infrared interrupter switches. The output signal need not be any more sophisticated than a simple binary signal indicating actuation of the sensor. 
     CCS Communication Interface  106 —This is the hardware through which the CCS Sensor Interface Unit  102  communicates with the POS Computer  101  or the CCS Multiplexer Unit  201 . The CCS Communication Interface  106  could be one of many different types including, but not limited to: serial, Universal Serial Bus, Ethernet, radio, wireless, telephone/modem, computer parallel port, etc. 
     Sensor Connection  107 —The Human Motion Sensor  103  may be connected to the CCS Sensor Interface Unit  102  via wires, radio link, infrared communications link, or the like. 
     CCS Multiplexer Unit  201 —A CCS Multiplexer Unit  201  may be used when more sensor inputs are needed than any one CCS Sensor Interface Unit  102  can provide. It can communicate with multiple CCS Sensor Interface Units  102  simultaneously. Event data from plural CCS Sensor Interface Units  102  may be passed through a CCS Multiplexer Unit  201  to POS Computer  102 . 
     Multiplexer Communications link to Computer  202 —This is a communication medium through which the CCS Multiplexer Unit  201  communicates with the POS Computer  101 . This communication link  202  could employ one or more different technologies including, but not limited to: serial, universal serial bus, Ethernet, radio, wireless, telephone/modem., computer parallel port, etc. When the POS Computer  101  is communicating with one or more CCS Sensor Interface Units  102 , an addressing protocol is employed to permit the POS Computer  101  to selectively communicate with a particular CCS Sensor Interface Unit  102 . 
     Communications Link from CCS Sensor Interface Unit to CCS Multiplexer Unit  203 —This link  203  is functionally the same as the link  105  from the CCS Sensor Interface Unit  102  to the POS computer  101  in systems not using the CCS Multiplexer Unit  201 . The CCS Multiplexer Unit  201  is transparent to the CCS Sensor Interface Unit  102  and enables the modular expansion of the system  200 . 
     Multiplexer Power Out  204 —The CCS Multiplexer Unit  201  can supply power to the attached CCS Sensor Interface Units  102 . This reduces the number of total power supplies required to one, thus reducing cost and the need for multiple AC outlets. 
     Power Supply  104 —This is an external source of power for either the CCS Multiplexer Unit  201  or CCS Sensor Interface Unit  102 . This will typically be an off the shelf power supply or could possibly be a battery. 
     As shown in FIG. 1, a simple installation of the exemplary system  100  includes a point of sale (POS) computer  101 , a customer conversion system (CCS) interface unit  102 , one or more sensors  103  and optionally an independent power supply  104  for the CCS interface unit  102 . 
     In the illustrated configuration, unit power is provided by power supply  104 . When a customer enters an establishment employing the system, the customer activates a sensor  103 . Sensor  103  is connected through a communication medium, such as a cable  107  or radio link (not shown) to CCS interface unit  102 . CSS interface unit  102  analyzes the activation and immediately sends data through a communication medium  105  to the POS computer  101 . The POS computer  101  receives notice of activation and increments its count of customers for the current interval. At the end of each predetermined interval (e.g. 1:30 p.m. for 30 minute intervals), counts for sensors are stored in a computer data file on the POS computer  101  or on a remote computer (not shown) with which the POS computer  101  may communicate from time to time. 
     Computer  101  may also request diagnostic or status information from the CCS Sensor Interface Unit  102  through communication medium  105 . The CCS Sensor Interface Unit  102  will respond with diagnostic data or status. 
     As shown in FIG. 3, the system may share sensors  103  with another device or system, such as a security system  301 . Unit power can be optionally provided by power supply  104 . A customer activates sensors  103 . Communication media  107  connect sensors  103  to interface unit  102 . Interface unit  102  analyzes the outputs and immediately sends data through communication medium  105  to computer  101 . Computer  101  receives the sensor output and increments its count for a current interval. As described above, the end of each interval (e.g., at 1:30 p.m. for 30-minute intervals), counts for sensors are stored in a computer data file. 
     Also described above, computer  101  may request diagnostic or status information through communication medium  105 . CCS Sensor Interface Unit  102  will respond with diagnostic data or status. 
     This configuration is attractive since extra wiring and sensors are not needed for the CCS. Communication medium  107  can be connected to the sensors  103  at the security system  301  panel, for example. 
     FIG. 2, mentioned earlier, illustrates an exemplary system  200  that uses two or more CCS interface units  102 . A multiplexer  201  is used to communicate data from the computer  101  to plural interface units  102 . Multiplexer  201  power may optionally be provided by a local power supply  104  provided for the purpose. Interface unit  102  power may be supplied either through multiplexer  201  or by one or more dedicated power supplies (not shown) provided therefor. In operation, a customer activates one of the sensors  103 . Sensor communication media  107  connect the sensors  103  to interface units  102 . Interface units  102  analyze signals received over communication media  107  and immediately sends data through communication link  203  to multiplexer  201 . Multiplexer  201  immediately forwards data through communication link  202  to computer  101 . Computer  101  receives signals indicating that one or more of the sensors have been activated and increments its count of customers for the current interval. At the end of each interval (e.g., at 1:30 p.m. for 30-minute intervals), counts for sensors are stored in a computer data file. 
     Computer  101  may request diagnostic or status information through communication link  202 . Multiplexer  201  will forward such a request through communication link  203  to one or more interface units  102 . Interface units  102  may be separately addressable using conventional techniques. An interface unit  102 , which has received such a request, will respond with diagnostic data or status through communication link  203  to multiplexer  201 . Multiplexer  201  will then forward the diagnostic or status data through communication link  202  and then to computer  101 . 
     As shown in FIG. 4, a variation of the embodiment of the invention illustrated in FIG. 2 may be arranged such that the sensors  103  are shared with another device or system in a manner similar to that discussed in connection with FIG.  3 . The system of FIG. 4 uses two CCS interface units  102  (more are possible) and shares four sensors  103  (more are possible) with another sensing device such as a security system  301 . The multiplexer  201  is used to connect the computer  101  to interface units  102 . Multiplexer  201  power may be provided by a local power supply  104 . Interface power may come from either the multiplexer  201  or from a dedicated power supply (not shown). In operation, a customer activates sensor  103 . Sensor communication medium  107  connects activation to interface unit  102 . Interface unit  102  analyzes sensor signals received over communication medium  107  and immediately sends data concerning those signals through a communication link  203  to multiplexer  201 . Multiplexer  201  then immediately forwards data through communication link  202  to computer  101 . When computer  101  receives data indicative of activation of a sensor  103  by a customer, increments its count of customers for the current interval. At the end of each interval (e.g., at 1:30 p.m. for 30-minute intervals), the computer  101  counts for all of the sensors  103  are stored in a computer data file. 
     Computer  101  may request diagnostic or status information through communication link  202 . Multiplexer  201  will forward request through communication link  203  to interface unit  102 . Interface unit  102  will respond with diagnostic data or status through communication link  203  to multiplexer  201 . Multiplexer  201  will forward diagnostic or status data through communication link  202  to computer  101 . 
     In order to discuss the details of the design of an exemplary CCS interface unit  102 , as shown in FIG. 5, several more definitions are useful. 
     Computer Data Interface  501 —This circuit includes devices to convert signals from a central processing unit  502  to be compatible with an external data communications medium. This interface can be either bi-directional or uni-directional. 
     Unit Power Indicator  503 —This is simply a visual or other indicator that relays status of power supply system  504 . This may consist of visible displays such as lamps, LEDs, LCDs, or any other visual device that changes state when correct power is applied. The Unit Power Indicator  503  may also be an audible device such as a speaker or electromechanical device such as a meter. The Unit Power Indicator  503  can also indicate correct power by an electrical signal or computer message, which is locally or remotely received and interpreted. 
     Central Processing Unit  502 —A logic chip or chips that monitor and control system functions. The exemplary embodiment uses a single chip microcontroller. 
     Sensor Diagnostic Indicator  505 —This is an indicator that communicates in a human-readable form, status of recent or present sensor activity. This may consist of visible displays such as lamps, LEDs, LCDs, or any other visual device that changes state when sensor activity is detected or sensor error is detected. The Sensor Diagnostic Indicator  505  may also be an audible device such as a speaker or electromechanical device such as a meter. Like the Unit Power Indicator  503 , the Sensor Diagnostic Indicator  505  can produce an electrical signal or computer message, which is then converted to human-readable form. 
     Sensor Interfaces  506 —This is the electronic circuitry that is connected to the sensors. The Sensor Interfaces  506  may be designed to detect switch contact closures and openings, solid state signals such as open collector transistors and logic outputs, changes in electrical current, changes in current and/or changes in voltage. 
     Optional Switch Output  507 —This output  507  is used to forward a switch closure to another switch receiving unit. This is useful when using one set of switches with 2 different sensing units. 
     Unit Configuration Method  508 —This is the collection of procedures by which a unit  102  is configured for proper operation. Parameters like switch polarity and sensitivity or switch timing might be set using this method. The method may include manipulating one or more switches that are set to a particular position to signify a particular setting. The method may also manipulate a momentary device like a switch that analyzes a sample switch activation and creates a timing method for monitoring switch during future activations. 
     Some additional definitions relate to the CCS Multiplexer Unit  201  of FIG.  6 . 
     Port Status Indicator  601 —The Port Status Indicator  601  communicates in human-readable form, the status of recent or present sensor activity received from interface units. This indicator  601  may consist of visible displays such as lamps, LEDs, LCDs, or any other visual device that changes state when sensor activity is detected or sensor error is detected. Indicator  601  may also be an audible device such as a speaker or electromechanical device such as a meter. This indicator may also produce an electrical signal or computer message which is interpreted either remotely or locally to produce a human-readable output. 
     Optional Port Power Outputs  602 —These outputs can supply power to attached CCS interface units. 
     Port Data Interfaces  603 —These Interfaces  603  include the electronic circuitry necessary to communicate with CCS Interface Units. 
     An exemplary CCS interface unit  102  is now described in connection with FIG.  5 . Unit power is received through input  509 . If necessary, power is converted by power supply  504  and provided to sections  501 ,  502 ,  503 ,  505 ,  506 ,  507  and  508 . Correct power condition is indicated by indicator  503 . 
     On power up, central processing unit  502  initializes its internal registers and prepares for operation. On a continuous or periodic basis, central processing unit  502  performs instructions directing configuration method  508  and sets its monitoring methods according. On a continuous or periodic basis, central processing unit  502  monitors sensor interface  506  for activity. If valid activity is detected, data is sent out or stored that represents a valid activation. Determination of a valid sensor activation may be represented on indicator  505 . Optionally, determination of a valid sensor activation may be represented on optional switch output  507 . 
     An exemplary CCS Multiplexer Unit  201  is now described in connection with FIG.  6 . 
     On power up, central processing unit  604  initializes its internal registers and prepares for operation. On a continuous or period basis, central processing unit  604  and optionally communications support circuitry monitor ports  603  for data sent by one of the CCS interface units (FIG. 2,  102 ). If sensor activation data is received, it is either stored and/or immediately forwarded to computer interface  605 . If sensor activation data is received, it may also be represented on indicator  601 . 
     Diagnostic requests can also be received by interface  605 . Such requests are then forwarded through port  603 . When a response is received through port  603 , it is forwarded through interface  605 . When a diagnostic request fails to produce a response at port  603 , the Central Processing Unit  604  may or may not initiate an error sequence, possibly causing an error code to be transmitted on interface  605 . 
     The exemplary embodiment of the CCS Sensor Interface Unit  102  has two inputs. It is designed to monitor up to two switch type sensors and report activation data to a computer. Other numbers of sensors could be monitored by alternative designs. 
     The CCS Sensor Interface Unit  102  of FIG. 5 may derive its power from a regulated 12-Volt DC Power Supply  504 . The supply  504  may be connected to the Unit  102  by any conventional means, such as a 5.5 mm by 2.1 mm power plug with negative center, or a screw terminal block for hard wiring power to the board when a power plug is not available. 
     The CCS Sensor Interface Unit  102  will incorporate a RS-232 serial port that is used to upload event and diagnostic data directly to a computer or indirectly through the CCS Multiplexer Unit  201  multiplexer to a computer. These connections have been described above. 
     Returning to FIG. 5, operation of the CCS Sensor Interface Unit  102  is now described. The exemplary CCS Sensor Interface Unit  102  connects to a computer with the same commercially available cable that is used with modems. Serial communication takes place using the following parameters. 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Baud Rate: 
                 1200 bits per second. 
               
               
                   
                 Data Bits: 
                 8 
               
               
                   
                 Stop Bits: 
                 1 
               
               
                   
                 Parity: 
                 None 
               
               
                   
                   
               
             
          
         
       
     
     Other types of communication and communication parameters can also be used, if desired. 
     The CCS Sensor Interface Unit  102  communicates according to the following modes. 
     Normal Operating Mode 
     When unit determines that a valid sensor activation has occurred, it will promptly send two data strings out its computer interface port. 
     The first data string is compatible with a first sensor monitoring application. The string is the same regardless of which sensor was activated and is therefore not capable of providing individual sensor totals. 
     The second data string is compatible with a proposed second sensor monitoring application. It will provide data that indicates which sensor input received the activation and therefore will facilitate counting of individual sensors. 
     The first sensor monitoring application ignores the second data string. 
     The second sensor monitoring application will ignore the first data string and use the second data string. 
     The CCS Sensor Interface Unit  102  does not have or need a Real Time Clock (RTC) in it. The receiving and collection of the above mentioned data strings is dependent on the monitoring software in the computer and therefore, the CCS Sensor Interface Unit  102  need not possess a time stamping capability. However, it is possible to implement aspects of the invention using a CCS Sensor Interface Unit  102  that does include an RTC that is used to time stamp data. 
     The data strings are automatically sent out when a valid activation occurs. According to one embodiment, the CCS Sensor Interface Unit  102  is not polled for new activation data by the computer. This eliminates a lot of communication overhead and simplifies the CCS Multiplexer Unit  301 . However, in some applications it may be desired to retrieve new activation data by polling one or more CSS Sensor Interface Units  102  connected to the CSS Multiplexer Unit  301  using conventional polling techniques. 
     Diagnostic Mode 
     The CCS Sensor Interface Unit  102  accepts requests from the computer for diagnostic status information. A minimum of the following information will be available: 
     Unit Type: e.g., 2 input or 4 input 
     Firmware Version: e.g., V 1.0 
     Mode Switch Settings 
     Current Sensor State 
     Fault Condition 
     During the brief diagnostic data request, switch activation data will not be sent to computer. Switch activations received during the processing of a diagnostic data request may be stored and then sent following the diagnostic sequence, or may simply be discarded, as desired by the designer. 
     Additional diagnostics may also be implemented. 
     The CCS Sensor Interface Unit  102  has a sensor interface specified as follows: 
     Number of Sensor Inputs: 2 
     Method of Connecting Sensor: 2-wire screw terminal block 
     Sensor Compatibility: Mechanical switch contact 
     Sensor Polarity: Can be Normally Open or Normally Closed 
     The CCS Sensor Interface Unit  102  requires that the sensor must be activated and stable for at least 75 milliseconds to be deemed a valid activation. Such a criterion prevents false activations due to switch bounce. Other times may be used, as required. 
     Preferably, the total resistance of sensor wire and the active sensor element, for example a switch, should not exceed 100 ohms. Other designs may accommodate greater or lesser sensor resistance values. 
     The exemplary Unit is designed to operate with switches that are dedicated exclusively to the CCS Sensor Interface Unit  102 . However, the skilled artisan will understand that designs are possible which share a sensor with a security system or other equipment, for example. 
     In order to accommodate a variety of sensor configurations, the exemplary CCS Sensor Interface Unit  102  includes three mode switches. The first mode switch sets compatibility with the sensor polarity. The second two mode switches set sensitivity, as follows. 
     Sensitivity is defined by a combination of Minimum Switch Activation Time and Minimum Time Between Activations. Minimum Switch Activation Time is the minimum time the switch is active and stable, i.e., not bouncing before being deemed a valid switch activation. Minimum Time Between Activations is the minimum time the switch must be inactive before a new activation will be considered. This filters out extra counts in situations where the sensor is prone to being activated more than once by the same customer. An example of four sensitivity settings possible using two switches is shown in the following table. 
     
       
         
               
               
               
             
           
               
                   
               
               
                   
                 *Minimum Switch 
                 *Minimum time 
               
               
                 Sensitivity 
                 Activation Time 
                 between Activations 
               
               
                 Setting 
                 (in milliseconds) 
                 (in milliseconds) 
               
               
                   
               
             
             
               
                 A 
                 100 
                 250 
               
               
                 B 
                  50 
                 100 
               
               
                 C 
                 250 
                 250 
               
               
                 D 
                 100 
                 100 
               
               
                   
               
             
          
         
       
     
     The exemplary CCS Sensor Interface Unit  102  provides visible indicators that are helpful during installation and ongoing troubleshooting of the system. Indicators are visible to the outside of the unit regardless of whether or not the access cover is present. 
     Some useful diagnostic indicators include power and sensor state. The power indicator simply glows when power is present and correct. The sensor state indicator may indicate a variety of conditions, as follows. During power up, each indicator blinks 3 times. This indicates basic system is operational. Each indicator blinks once for each valid switch activation. Continuous blinking of the indicator shows that a fault condition exists. Blinking stops when the fault condition is corrected. A fault condition is assumed to exist when the sensor is in the activated state for more than 10 seconds. A fault condition will most commonly be caused by a mismatch between the sensor switch type and the Polarity mode switch. Other examples of fault conditions might be an open connection in a Normally Closed configuration or a wire short in a Normally Open configuration. The time duration of the condition deemed a fault may be set at other than 10 seconds. 
     In operation, any of the embodiments of FIGS. 1-4 cause the POS computer or other computer to receive signals indicating sensor activations. Such sensor activations are stored by the computer, as follows. Each activation may be stored as a record in a computer file together with a time-stamp indicating when it occurred. Alternatively, activations occurring within a defined interval may be tallied up and the total stored as a record in a computer file together with a time-stamp indicating a relevant time, such as when the interval began or ended, or perhaps both. In both cases, a time when an activation occurred is recorded, with varying degrees of time resolution or granularity. Computations can then be performed to obtain, for example, statistical models of relationships between numbers of customers served and numbers or dollar values of sales made. 
     The present invention has now been illustrated by the foregoing descriptions of several embodiments and aspects thereof. Numerous variations and modifications contemplated as within the invention should now be evident to the skilled artisan. Therefore, the invention is limited only to the scope of the appended claims and equivalents thereto, when properly construed.