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.