The term transponder (short-for Transmitter-responder)means an automatic device that transmits a predetermined message in response to a predefined received signal. These car year, make and models have keys with transponders hidden inside the plastic head of the key. The owner of the car may not even be aware that the transponder is there because there are no buttons to press. When a key is inserted into the ignition lock cylinder and turned, the car's computer sends a radio signal to the transponder. Unless the transponder replies with a valid code, the computer will not allow the engine to be started. Transponder keys have no battery; they are energized by the radio signal itself. When you attempt to start the vehicle, the onboard computer sends out a signal that is picked up by the transponder in the key. The transponder then returns a unique signal to the vehicle's computer, giving it the ok for the vehicle to start and continue to run. This all happens in less than a second, and is completely transparent to the vehicle operator. It is a very effective system that does its job without the vehicle owner having to think about it, or modify his / her usual routine. This system was introduced to help reduce vehicle crime. If the transponder key is missing or faulty the car will not start.