•What is a transponder?

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–When you go to get into your car most keys have a “chip” hidden inside the plastic head of the key. This so called chip is a transponder

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–When a key is inserted into the ignition and turned, the car's computer sends a radio signal to the transponder

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–Unless the transponder replies with a valid code, the computer will not allow the engine to start

 

•With aircraft though, depending on the “type of interrogation”, the transponder will answer with a transponder code