Abstract: A theft detection and location system for aircraft utilizing both a conventional aircraft transponder/encoder and a dedicated transponder/encoder. The dedicated transponder is fixed on an alarm code which when transmitted in response to interrogation signals from ground stations, alerts air traffic controllers that the aircraft has been stolen. The system includes electronic switching devices which automatically enable the dedicated transponder to be activated each time an aircraft electrical master switch is turned on. An arming device is provided for activating the dedicated transponder in response to a predetermined condition. The dedicated transponder will continue to function even if the entire aircraft electrical system is turned off since the electronic switching device directly couples the dedicated transponder to the aircraft battery. A disarming device is provided in order to deactivate the dedicated transponder and in turn activate the conventional transponder.