Abstract:
This document discloses various systems and methods for reducing the likelihood of leaving an unattended child behind in an infant/child seat in a vehicle.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This patent application claims the benefit of priority, under 35 U.S.C. Section 119(e), to U.S. Provisional Patent Application Ser. No. 60/305,110, filed Jul. 12, 2001, the disclosure of which is incorporated herein by reference in its entirety. 

   TECHNICAL FIELD 
   This document relates generally to a warning system for detecting the presence of an occupant in a vehicle, and particularly, but not by way of limitation, to a warning system for sensing a child left in an infant seat in a vehicle. 
   BACKGROUND 
   Bringing home new baby is usually a joyful occasion. The addition of new family member, however, can be stressful on a family as the presence of a new family member changes the family dynamics. Also, with a new baby in the home, parents or caretakers are often seriously sleep deprived due to an infant&#39;s irregular feeding and sleeping schedules. A long period of sleep deprivation can have a significant effect on a person&#39;s memory. Tragically, every year infants die or are seriously injured to due a driver forgetting that an infant is in the back seat of a car, and leaving the vehicle for a long period of time, such as while they are working. If the weather is either very hot or very cold, the infant can perish prior to anyone becoming aware of the dangerous situation. According to one report, from the years 1996 to 2000 in the United States, more than 120 children died from heatstroke in a vehicle (although not all of these children were infants left behind in carseats; some were children that climbed into parked cars but then couldn&#39;t get out on their own). 
   A system for detecting whether a child car seat harness is locked is discussed in U.S. Pat. No. 5,581,234 to Emery et al., entitled INFANT VEHICLE SEAT ALARM SYSTEM, which is incorporated herein by reference in its entirety. 
   A system for detecting whether a child has been left behind in a school bus is discussed in U.S. Pat. No. 5,243,323 to Rogers, entitled SCHOOL BUS ALARM SYSTEM, which is incorporated herein by reference in its entirety. 
   A system for preventing children from becoming inadvertently locked within a vehicle is discussed in U.S. Pat. No. 5,793,291 to Thornton, entitled CHILD ALERT SYSTEM FOR AUTOMOBILES, which is incorporated herein by reference in its entirety. The system uses a motion detector to detect the presence of a child or pet within a locked vehicle. While this system provides some advantages, particularly in the case of older children that may inadvertently lock themselves in a vehicle while playing, it fails to protect children who have been left asleep in their child seats and are not capable of sufficient activity to set off a motion detector. Such infants may continue sleeping and may become dehydrated and comatose without ever waking, and therefore, they may not be detected by a motion detector. 
   A system for preventing children from being left behind in an infant car seat is discussed in U.S. Pat. No. 5,949,340 and U.S. Pat. No. 6,104,293 to Rossi, each entitled WARNING SYSTEM FOR DETECTING PRESENCE OF A CHILD IN AN INFANT CAR SEAT, and each of which is incorporated by reference herein in its entirety. This system generates a warning when an infant is present and the vehicle ignition system has been turned from “on” to “off.” Detecting the state of an automotive ignition system, however, may be difficult to implement. Such ignition detection may require complicated electronic components, which may be different for different automobile models. As a result, such a system may be difficult to bundle with an infant car seat, which is often, but not always, purchased separately from the vehicle. Therefore, such a system may not gain the widespread consumer acceptance that is desired to avoid the potential tragedy that may result from leaving a child behind in an infant car seat. The present inventors have recognized, therefore, that there is an unmet need for an improved system for avoiding such tragedy. 
   SUMMARY 
   This document discloses various systems and methods for reducing the likelihood of leaving an unattended child behind in an infant/child seat in a vehicle. 
   A first illustrative example includes a warning system for detecting a child left in an child car seat in a vehicle. In this example, the system comprises a child car seat, a child occupant sensor, a temperature sensor, and an alarm. The child occupant sensor includes an input to detect a child in the child car seat, and an output providing a signal representative of whether a child is present in the child car seat. The temperature sensor includes an input to detect an ambient vehicle temperature, and an output to provide a signal responsive to the ambient vehicle temperature. The alarm is coupled to the child occupant sensor output and the temperature sensor output. The alarm is configured to provide a warning using information about whether the child is present in the child car seat and the ambient vehicle temperature is outside an acceptable range. 
   The system of first example may include other variations. In one embodiment, the system may include a comparator circuit and a control circuit. The comparator circuit is coupled to the output of the temperature sensor. The comparator circuit includes at least one of high and low temperature thresholds. The comparator includes an output to provide a signal indicating whether the ambient vehicle temperature is outside the acceptable range. The control circuit is coupled to the output of the comparator and the output of the child occupant sensor. The control circuit includes a timer to determine whether the child has been in the seat for a predetermined period of time at a temperature outside the acceptable range, and an output to provide a responsive alarm activation signal. The alarm is coupled to the output of the control circuit to provide an alarm responsive to the alarm activation signal. 
   In other variations, the alarm is remote from the control circuit and communicatively coupled thereto. The alarm may include a wireless telephony device. The system may include an alarm disabling switch. The alarm may be coupled to at least a portion of a vehicle navigation system. The alarm may include a global positioning system (GPS) device. 
   In other variations, the alarm is communicatively coupled to a vehicle remote entry device to receive a door-locking signal. The alarm is also coupled to the child occupant sensor. The alarm is configured to provide a warning using information from the child occupant sensor indicating that the child seat is occupied and the door-locking signal indicating that the door is being locked. In a further variation, the alarm includes a signal strength detector configured to detect a distance between a portion of the vehicle and the remote entry device. The alarm is configured to use the distance in providing a responsive warning. 
   In other variations, the system further comprises a driver occupant sensor. The driver occupant sensor including an input to detect a driver in a driver&#39;s seat. The alarm is configured to provide a warning using information about whether the driver is present in the driver&#39;s scat. 
   In other variations, the alarm is configured to actuate at least one of unlocking and opening at least one of a door and a window of the vehicle. 
   A second illustrative example discloses a warning system for detecting a child left in an child car seat in a vehicle. The system comprises a child car seat, a child occupant sensor, and a remote entry device. The child occupant sensor includes an input to detect a child in the child car seat. The child occupant sensor includes an output providing a signal representative of whether a child is present in the child car seat. A remote entry device is communicatively coupled to the child occupant sensor. The remote entry device is configured to trigger a warning using information about whether the child is present in the child car seat. 
   In other variations, the remote entry device includes a user input device configured to lock a door of the vehicle. The remote entry device is configured to trigger a warning if the child is present in the child car seat when the user input device is activated to lock the door of the vehicle. In a further embodiment, the remote entry device is configured to trigger a warning using information about whether the child is present in the child car seat and information about a distance between the remote entry device and the vehicle. 
   In other variations, the system comprises a temperature sensor. The temperature sensor includes an input to detect an ambient vehicle temperature and an output to provide a signal responsive to the ambient vehicle temperature. The alarm is configured to provide a warning using information about whether the child is present in the child car seat and using the ambient vehicle temperature. 
   In other variations, the alarm is remote from the child car seat and is communicatively coupled thereto. In one embodiment, the alarm includes a wireless telephony device. In another embodiment, the system includes an alarm disabling switch. In another embodiment, the alarm is coupled to at least a portion of a vehicle navigation system. In another embodiment, the alarm includes a global positioning system (GPS) device. 
   In other variations, the alarm includes a signal strength detector. The signal strength detector is configured to detect a distance between a portion of the vehicle and the remote entry device. The alarm is configured to use the distance in providing a responsive warning. 
   In other variations, the system further comprises a driver occupant sensor. The driver occupant sensor includes an input to detect a driver in a driver&#39;s seat. The alarm is configured to provide a warning using information about whether the driver is present in the driver&#39;s seat. In one embodiment, the alarm is configured to actuate at least one of unlocking and opening at least one of a door and a window of the vehicle. (This may, however, be restricted to an excessively hot ambient vehicle temperature; an excessively cold ambient vehicle temperature does not trigger opening a door/window, in one embodiment). 
   A third illustrative example discloses a warning system for detecting a child left in an child car seat in a vehicle. In this example, the system comprises a child car seat, a child occupant sensor, a driver occupant sensor, and an alarm. The child occupant sensor includes an input to detect a child in the child car seat, and an output providing a signal representative of whether a child is present in the child car seat. The driver occupant sensor includes an input to detect a driver in a driver&#39;s seat. The driver occupant sensor includes an output providing a signal representative of whether a driver is present in the driver&#39;s seat. The alarm is communicatively coupled to the child occupant sensor and the driver occupant sensor. The alarm is configured to provide a warning using information about whether the child is present in the child car seat and whether the driver is present in the driver&#39;s seat. In another variation, the system includes an alarm disabling switch. 
   A fourth illustrative example discloses a warning system for detecting a child left in an child car seat in a vehicle. The system comprises a child car seat, a child occupant sensor, a driver door sensor, and an alarm. The child occupant sensor includes an input to detect a child in the child car seat, and an output providing a signal representative of whether a child is present in the child car seat. The driver door sensor includes an output providing a signal representative of whether a driver&#39;s door is open. The alarm is communicatively coupled to the child occupant sensor and the driver occupant sensor. The alarm is configured to provide a warning using information about whether the child is present in the child car seat and whether the driver&#39;s door is open. In another variation, the alarm includes an alarm disabling switch. 
   A fifth illustrative example discloses a method. In this example, the method includes detecting whether a child is present in a child car seat in a vehicle, detecting an ambient vehicle temperature, and providing an indication of whether a child is present in the child car seat at an ambient temperature outside an predetermined range. 
   In other variations, the method includes providing an indication of whether a child is present in the child car seat at an ambient temperature outside a predetermined range for a time period that exceeds a predetermined duration. In another embodiment, the method includes wirelessly communicating the indication to a remote location. In another embodiment, the method includes at least one of unlocking and opening at least one of a door and a window of the vehicle using the indication. 
   A sixth illustrative example includes a method. In this example, the method includes detecting whether a child is present in a child car seat in a vehicle, detecting a locking of a vehicle door, and providing an indication of whether a child is present in the child car seat upon the locking of the vehicle door. 
   In other variations, the method includes detecting a locking actuated by a remote entry device. In one embodiment, the method includes detecting a distance between the remote entry device and the vehicle, and in which the providing the indication includes also using the distance in determining whether to provide the indication. In another embodiment, the method includes wirelessly communicating the indication to a remote location. In another embodiment, the method includes at least one of unlocking and opening at least one of a door and a window of the vehicle using the indication. 
   An seventh illustrative example includes a method. In this example, the method includes detecting whether a child is present in a child car seat in a vehicle, detecting whether a driver is present in a driver&#39;s seat in the vehicle, and providing an indication of whether a child is present in the child car seat when the driver leaves the driver&#39;s seat. 
   In other variations, the method includes wirelessly communicating the indication to a remote location. In one embodiment, the method includes at least one of unlocking and opening at least one of a door and a window of the vehicle using the indication. 
   A eighth illustrative example discloses a method. In this example, the method includes detecting whether a child is present in a child car seat in a vehicle, detecting an opening of a driver&#39;s door of the vehicle, and providing an indication of whether a child is present in the child car seat when the driver&#39;s door is opened. 
   In other variations, the method includes wirelessly communicating the indication to a remote location. In one embodiment, the method also includes at least one of unlocking and opening at least one of a door and a window of the vehicle using the indication. 
   Other aspects of the disclosed systems, devices, and methods will become apparent upon reading the following detailed description and viewing the drawings that form a part thereof 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, which are offered by way of example, and not by way of limitation, and which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. Like numerals having different letter suffixes represent different instances of substantially similar components. 
       FIG. 1  is a schematic drawing illustrating generally an example of portions of a system sensing a child left behind in an infant seat in a vehicle and a portion of an example environment in which the system is used. 
       FIG. 2  is a block diagram illustrating generally an example of portions of a warning module. 
       FIG. 3  is a block diagram illustrating generally another example of portions of a warning module. 
       FIG. 4  is a block diagram illustrating generally an example of portions of an example transceiver in a warning module. 
       FIG. 5  is a block diagram illustrating generally an example of portions of a warning module including a driver occupant sensor. 
       FIG. 6  is a block diagram illustrating generally an example of portions of a warning module including a driver door sensor. 
   

   DETAILED DESCRIPTION 
   In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents. In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. 
   In this document, the terms “transceiver,” “transceiving,” and “transceiver” refer to transmitting and/or receiving data. That is, these terms include all of structures and methods of: (1) transmitting, but not receiving; (2) receiving, but not transmitting; and, (3) both transmitting and receiving. 
     FIG. 1  is a schematic drawing illustrating generally an example of portions of a system sensing a child left behind in an infant seat in a vehicle, and a portion of an example environment in which the system is used. This example illustrates an infant seat  100  and a warning module  102 . Warning module  102  is either integrally formed with seat  100 , such as to a back and/or base portion of seat  100  or, alternatively, a portion of warning module  102  is located remotely from seat  100  and coupled thereto. In this example, seat  100  includes a base  104  that is attached to a rear seat or other portion of the vehicle, such as using a vehicle seat belt or other fixation technique. Seat  100  is releasably attached to base  104  using known techniques. Alternatively, base  104  need not be included, and seat  100  is fastened to the vehicle without the intermediate base  104 . Moreover, seat  100  can be configured either as a forward-facing or rear-facing car seat using known techniques, as an infant seat integrated with the vehicle itself, and/or as a booster seat for an older child. In this example, seat  100  includes a harness and associated belts for securing a child to reduce the risk of injury to the child in the event that the vehicle is in a collision or other accident. 
     FIG. 2  is a block diagram illustrating generally an example of portions of warning module  102 . In this example, warning module  102  includes: an occupant sensor  200 ; temperature sensor  202 ; a comparator  204 ; a logic circuit, state machine, microprocessor, or other control circuit  206 ; a timer circuit  208 ; and an alarm  210 . Occupant sensor  200  detects whether a child is present in seat  100 , and provides a resulting output indicator, at node/bus  212 , to control circuit  206 . Temperature sensor  202  (for example, a thermistor, thermocouple, semiconductor circuit, etc.) detects ambient temperature in the vehicle and provides, at node/bus  214 , a signal indicative thereof to comparator  204 . Comparator  204  compares the received temperature signal at node/bus  214  to one or both of a high temperature threshold value and/or a low temperature threshold value defining an acceptable temperature range between these temperature extreme thresholds. Comparator  204  provides to control circuit  206 , at node/bus  216 , a signal indicating whether the ambient vehicle temperature is within or outside the acceptable temperature range. Control circuit  206  performs executable steps, or includes hardwired logic, to operate so that if seat  100  is occupied and the ambient vehicle temperature is outside the acceptable range, timer  208  is reset to initiate the subsequent measurement of time. If seat  100  is occupied and the ambient vehicle temperature remains outside the acceptable range for a predetermined period of time, logic or other control circuit  206  provides a signal, at node/bus  218 , that a potentially dangerous alarm condition exists, and activates alarm  210 . 
   In one example, alarm  210  first provides an audible and/or visual indication within the vehicle that a child has been exposed to temperature extremes for the predetermined period of time. In another example, alarm  210  includes a wireless communication device that wirelessly communicates the alarm condition to a remote device  220 . Remote device  220  includes a portion that is mounted to the exterior of the vehicle (e.g., under the hood in the engine compartment of the vehicle), or even in the interior of the vehicle. In response to the alarm condition received from alarm  210 , remote device  220  provides an audible and/or visual alarm, or is otherwise configured to attract the attention of any nearby people outside the vehicle. 
   In another example, alarm  210  includes a wireless telephony device that communicates through a wireless telephone network to a remote device  220 . In this example, remote device  220  may be a mobile or other telephone number of a caregiver, a “911” operator, an emergency monitoring service provider, or a prioritized preprogrammed list of several such or other telephone numbers to be dialed in the event of such an emergency. Where alarm  210  also includes an indicator within the vehicle, such actions summoning emergency personnel or other caregivers may be suppressed by the driver, upon hearing the interior alarm indicator, disabling subsequent alarm actions by pressing switch  222 . 
   In a further example, alarm  210  includes a connection or wireless transmitter coupled to an onboard vehicle navigation system serving as remote device  220 . In this example, the vehicle navigation system is capable of wirelessly communicating with a further remote user, emergency personnel, or emergency monitoring service. Alarm  210  provides an alert signal to the vehicle navigation system, which is, in turn, communicated to the remote user or service. Examples of suitable vehicle navigation systems are commercially available. Some vehicle navigation systems also include a global positioning system (GPS) for further communicating the location of the vehicle to the remote user or service so that emergency personnel can be summoned. Alternatively, such functionality of the vehicle navigation system is incorporated within alarm  210  itself, which communicates alert and location information to a remote device  220 , where the remote device  220  is a remote user or monitoring service. 
   In a further example, warning module  102  includes a device for disabling the alarm  210 , such as on/off switch  222 . In yet another example, warning module  102  includes a power source  224 , such as a rechargeable or other battery, a cigarette lighter or other adapter to receiver power from the vehicle electrical system, or any other suitable energy source. 
     FIG. 3  is a block diagram illustrating generally another example of portions of a warning module  102 . This example includes a vehicle remote entry device  300  (sometimes referred to as a keyless entry device) for locking and unlocking vehicle doors by wirelessly communicating information to a companion vehicle transceiver  301  at the vehicle. Vehicle transceiver  301  is coupled to a vehicle door lock control actuation device  310  and a vehicle horn actuation device  312 . 
   In this example, warning module  102  includes a transceiver  302  that configured to receive the wireless signal from remote entry device  300  that triggers locking of the vehicle doors. Transceiver  302  communicates, via node/bus  304 , a signal to control circuit  306  that indicates that the vehicle doors are being locked. Occupant sensor  200  is also coupled, via node/bus  308 , to controller  306  to communicate a signal indicating whether seat  100  is occupied. If controller  306  detects that the car doors are being locked and seat  100  is still occupied, it communicates a signal to vehicle receiver or transceiver  301  to activate the vehicle horn actuation device  312  to sound the vehicle horn or other alarm. This alerts the nearby user of the remote entry device that a child is still in the car seat. The horn tone could be the same, or a different tone, from that typically activated upon locking the car doors, or upon pressing the “alarm” button on the remote entry device. If the horn is normally sounded upon locking the car doors, for example, then the alarm condition signaled by warning module  102  to vehicle transceiver  301  may include a longer audible alarm or other distinguishing feature to alert the user that a child is still in the car seat. In a further example, the signal from transceiver  302  to vehicle transceiver  301  optionally also triggers a responsive signal, from vehicle transceiver  301  to vehicle lock control device  310 , that unlocks one or more vehicle doors or prevents such doors from being locked. This further example could be temporarily disabled by the user, for that particular instance of locking the vehicle doors, by applying disable switch  222  to override such a function. In a further example, transceiver  302  is also capable of receiving a similar signal from a transceiver coupled to a power door lock mechanism at (rather than remote from) the vehicle. 
   In a further example, remote device  220  of  FIG. 2  is implemented as the illustrated vehicle transceiver  301  and horn actuation device  312  illustrated in FIG.  3 . Other combinations of  FIGS. 2 and 3 , and/or other figures in this document are also possible. 
   In a further example, as illustrated in the block diagram of  FIG. 4 , transceiver  302  includes a signal strength detector circuit  400  for detecting the strength of the wireless signal provided by remote entry device  300 . In this example, the received signal strength is used to determine the distance between the vehicle driver (carrying the remote entry device  300 ) and the vehicle itself. In one example, this distance is determined by receiving the output from signal strength detector  400  at a comparator  402 , comparing the signal strength to a predetermined value, and outputting a responsive signal that indicates whether the signal strength has fallen below the predetermined value and, therefore, the driver is determined to have gone beyond the allowable distance from the vehicle with the child still in seat  100 . 
   In this example, controller  306  operates such that transceiver  302  alerts vehicle receiver or transceiver  301  if the occupant sensor  200  indicates that a child remains in seat  100 , and the physical distance of remote entry device  300  (and, presumably, that of the driver carrying it) exceeds the predetermined threshold value (e.g., 25 feet), as determined from the received signal strength. Vehicle transceiver  301 , in turn, provides a signal to vehicle horn actuation device  312  for sounding the vehicle horn and optionally provides a signal to vehicle lock control device  310  for unlocking (and/or opening, in some vehicles which have such remote entry device activated automatic door-opening capability) one or more of the vehicle doors. 
   In a further example, in which the alarm is triggered by detecting the signal from remote entry device  300  to lock the vehicle doors when the child is in seat  100 , activation of the alarm also dependent upon the received signal strength. In this example, if the received signal strength exceeds the predetermined threshold value, the act of locking the vehicle doors using the remote entry device  300  does not trigger the alarm. This suppresses the alarm from being sounded when remote entry device  300  is used to lock the doors from within the vehicle, or when the remote entry device is in the immediate vicinity of the vehicle. 
     FIG. 5  is a block diagram illustrating generally an alternative example of portions of warning module  102 . This example includes a child occupant sensor  200 A and a driver occupant sensor  200 B. Driver occupant sensor  200 B is located at the driver seat of the vehicle. Each of child occupant sensor  200 A and driver occupant sensor  200 B are electrically connected or wirelessly coupled to other portions of warning module  102 , such as a logic circuit, state machine, digital microprocessor or microsequencer, or other suitable controller circuit  500 . Control circuit  500  is configured so that when child occupant sensor  200 A indicates that a child is in seat  100 , and driver occupant sensor  200 B indicates that the driver gets up from the driver seat, a responsive signal is provided by control circuit  500  to reminder alarm  502 . Reminder alarm  502  is located within and/or outside the vehicle, and provides a visual indication, an audible tone, and/or a voice message reminding the driver to remove the child from seat  100 . A disabling switch is electrically or wirelessly coupled to control circuit  500  to suppress the reminder alarm  502  (such as if the child is sleeping and the driver does not want to wake the child). In order to direct the driver&#39;s conscious attention to the child in such a situation, in one example, the disabling switch is located on seat  100  in close proximity to the child, but also within reach of the driver from the front driver seat. 
     FIG. 6  is a block diagram illustrating generally an alternative example portion of a warning module  102 . This example includes a child occupant sensor  200 , and a driver door sensor  600 , each communicating responsive signals to control circuit  601 . In this example, control circuit  601  is configured so that when child occupant sensor  200  indicates that a child is in seat  100 , and driver door sensor  600  indicates that the driver door has been opened, a responsive signal is provided by control circuit  601  to reminder alarm  502 . Reminder alarm  502  is located within and/or outside the vehicle, and provides a visual indication, an audible tone, and/or a voice message reminding the driver to remove the child from seat  100 . A disabling switch is electrically or wirelessly coupled to the control circuit  601  to suppress the reminder alarm  502  (such as if the child is sleeping and the driver does not want to wake the child). In order to bring the driver&#39;s conscious attention to the child in such a situation, in one example, the disabling switch is located on seat  100  in close proximity to the child, but also within reach of the driver from the front driver seat. 
   In various embodiments, occupant sensor  200  includes a weight or pressure sensor device in or attached to seat  100 . Examples of weight and pressure sensors for vehicle seats are found in U.S. Pat. No. 6,243,643; U.S. Pat. No. 6,259,167; U.S. Pat. No. 6,223,606; U.S. Pat. No. 6,070,115; U.S. Pat. No. 6,024,378; U.S. Pat. No. 5,971,432; U.S. Pa. No. 5,848,661; U.S. Pat. No. 5,640,145; and U.S. Pat. No. 5,821,633, each of which is incorporated by reference in its entirety. Some of these sensors include pressure sensing switches located in the seat cushion, under the seat cushion, in the headrest, and/or in or under a backrest cushion. For infants, the weight to be determined is, for example, but not by way of limitation, in the range of about 1 to about 30 pounds, in the range of about 2 to about 25 pounds, or in the range of about 5 to about 20 pounds. The weight of the infant may be greater than or less than these values, as the infant may not be positioned such that her or his full body weight registers on or with the sensor. 
   Another example of occupant sensor  200  includes a visual or other electromagnetic radiation detector, such as a camera. Examples are found in U.S. Pat. No. 6,198,998; U.S. Pat. No. 5,983,147; U.S. Pat. No. 6,005,958, each of which is incorporated by reference in its entirety. The camera may be mounted in a number of different positions in the vehicle, such as over the front wind shield or on the roof. See, e.g., U.S. Pat. No. 6,014,602, which is incorporated by reference herein in its entirety. Another example occupant sensor  200  includes an ultrasound transmitter and/or receiver. See, e.g., U.S. Pat. No. 6,029,105, which is incorporated by reference herein in its entirety. Another example of occupant sensor  200  includes an electromagnetic field sensor. See, e.g., U.S. Pat. No. 5,605,348, which is incorporated by reference herein in its entirety. Other types of transmitter and/or receiver sensor(s) are also included. See, e.g., U.S. Pat. No. 5,802,479, which is incorporated herein by reference in its entirety. Moreover, a combination of the above sensors or other sensors can be used to implement occupant sensor  200 . See, e.g., U.S. Pat. No. 6,026,340, which discusses a combination infrared and ultrasound sensor as a multi-sensor and a combination thermal and acoustic sensor, and which is incorporated herein by reference in its entirety. 
   Examples of remote entry device  300 , vehicle transceiver  301 , and associated vehicle components to which vehicle transceiver  301  interfaces, are discussed in U.S. Pat. No. 5,600,302, U.S. Pat. No. 6,236,333, and U.S. Pat. No. 6,259,362, each of which is incorporated by reference herein in its entirety. 
   While the above examples have treated the particular problem of leaving a child behind in an infant seat, it is understood that these techniques are equally applicable to sense and warn whether any occupant (e.g., driver or other passengers) has been left behind in a vehicle seat, which need not be a child seat. Moreover, the terms infant seat and child seat in this document include child booster seats for older children. Furthermore, the infant, child, or booster seats referred to herein need not be limited to removable seats, but also include such seats that are built in to the vehicle itself, including such seats that are also capable of seating an adult. 
   It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-discussed embodiments may be used in combination with each other. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.”