Motor vehicle anti-theft deterrent system with ignition key lock

摘要

The rotatable lock barrel (32) for starting the engine has an integral permanent magnet (38) which activates one of two Hall effect devices (40) when the lock is turned into the "start" position. The first Hall effect device connects two resistances (46, 48) into the security circuit and the resulting voltage drop across the resistances is compared with a programmed value to release the security locks. The second Hall effect device (42) is not affected by the position of the lock barrel magnet. If an external permanent magnet is used to try and release the security circuit then the second Hall effect device is also activated. This alters the effective resistance of the two resistances and produces a different voltage drop. The security circuit is not released in this instance.