RFID buckle closure and presence sensor system for safety childseat

In the preferred embodiment of the present invention a passive, wireless, RFID-based wireless buckle-closure sensor determines whether the buckle of a child safety seat is secured. Sensors also are provided to determine if the child is in the seat, the temperature and if the vehicle is in operation, and alarms are sounded if an unsafe condition is detected by the system. Child safety seats utilize a 3-point or 5-point locking-mechanism for seat belt and harness restraints. The locking-mechanism requires that metal belt/harness components latch together and are released by depression of a lock-mounted release button. In the preferred embodiment of the present invention a passive RF transponder is affixed to the buckle. Essentially the RF transponder comprises an RFID device without a data component. The RF transponder is interrogated by a frequency-scanning reader, which determines the resonant frequency of the transponder. The resonant frequency of the transponder is affected by the presence of the metal fittings local to the RF transponder. Thus, since the major components of the buckle and latch are metal, the detection of the change in the resonant frequency of the transponder, also referred to as "detuning," permits the determination of the state of the belt/harness buckle-latched or unlatched. This sensing is wireless, unobtrusive, and requires only a passive component be attached to the buckle. Further disclosed is a method of determining the status of a child in a child safety seat, including: whether or not a child is in the seat, whether or not the belt/harness buckle is latched, whether the vehicle's engine is in operation, and whether or not the surrounding temperature exceeds the temperature range. If an unsafe condition is detected, an alarm is activated.