Transponder keys are devices designed to transmit a radio signal from a handheld device to a remote receiver. They’re most commonly used to unlock and start vehicles, though they’re also used in things like gate openers and keyless entry systems. Each one is programmed to only start a specific vehicle, to reduce the possibility of theft. There are a number of ways to bypass transponders, however, most of which can be done with inexpensive equipment.
In vehicle used transponder keys, introduced in 1995, the transmitter unit consists of a small microchip in the plastic part of a key. The microchip has a unique serial number, which is set during its initial programming. When a person wants to unlock or start a car, the chip sends a request to the car for it to validate the serial number and turn off the engine’s immobilizers. If the car doesn’t recognize the number, it will remain locked and immobilized. A key that has not been programmed can still turn the engine over, but it won’t be able to start it, since the immobilizers will still be activated.