Definition : Emitter-receiver device that responds automatically to a radar, radio or sonar signal and allows a vehicle to be located, identified and guided.
1. Transponders were initially used in air and sea navigation, but are also used in intelligent transport systems, in particular to facilitate the sorting of commercial vehicles at a roadside check facility or toll station.
2. In the automobile industry, a transponder may also be used to transform an ignition key into an electronic anti-theft device [OQLF].