Transponder Key

     A transponder is a device that receives a signal，alters it and then retransmits thesignal in an altered state to another device. Some late-mode anti-theft systems now uses atransponder built into the ignition key. It is designed to prevent thieves with a knowledgeof electronics from overriding the security system.

    Every time the vehicle is started，the on-board computer sends a signal to the ignitionkey. The key's transponder alters this signal and sends it back to the computer. Thetransponder sends a new signal to the computer on every startup. This prevents a thieffrom auplicating the key as easily.

    The computer knows what that key's circuitry should do with each signal variation. Ifthe computer does not obtain the correct return signal from the key, it disables the startingand engine support systems so the vehicle cannot be driven.

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