Abstract: A transponder identification system comprising a plurality of transponders and an interrogation device arranged to identify each of the transponders by transmitting successive interrogation signals according to a systematic search strategy, wherein the search is truncated where the interrogation device receives fewer than a predetermined number of different responses from the transponders, to a transmitted interrogation signal.

Abstract: A radio communication system for a vehicle, which may act as an interrogation unit monitoring for the presence of a valid transponder or may act as a transponder to an external interrogation unit, includes an aerial incorporated in the circumferential part of the steering wheel of the vehicle and an on-board electronic system mounted in at least one spoke and/or in the central hub part of the steering wheel.

Abstract: Access control equipment includes an interrogation unit which emits an interrogation signal, and a plurality of transponders, each transponder having a stored identity code different from that of the other transponders. This identity code includes a plurality of fields each holding a selected information bit. The interrogation signal is controlled so as simultaneously to interrogate the fields of all transponders within range in a serial manner. A group reply signal is sent back to the interrogation unit from any transponder having, in the field being interrogated, a bit matching that required by the interrogation signal. The interrogation unit is arranged to determine, from the series of received reply signals, the identity of each and every valid transponder within range.