Vehicle security system with electronic coded key - gives alarm if doors are opened or if ignition is operated without correct key

When set to the 'alert' state, the vehicle security system gives an alarm if any of the doors are opened, even with a key, or if the ignition circuits are energised by any means. The system can only be switched to the 'passive' state by inserting a special coded key in the lock. The special key contains a circuit which generates a number of frequencies simultaneously, chosen from a wide frequency range, to form a combination. The key has contacts which mate with contacts in the lock to provide power for the key and transmit the combination to a detector. The system is switched to 'alert' by locking the door with the special key. A timer can be started, using the key, to permit servicing for a limited period using an uncoded pass key.