HIGH - TECH CAR KEYS
A transponder stands for (transmitter-responder). In simplest terms it's a radio transmitter/ receiver device that is programmed in to the computer of the car. If the corresponding key to the computer is not used on the car, the care will not start.
Some car manufacturers like Land Rover and Volkswagen use a 'switchblade' key where the key is spring-loaded out of the fob when a button is pressed.
Some car manufacturers like Mercedes - Benz uses a key that, rather than have a cut metal piece to start the car, uses an encoded infrared beam that communicates with the car's computer. If the codes match, the car can be started.