US Patent 7327231 Failsafe disable in a vehicle security system

The disclosed device is an additional, normally-closed relay positioned in line with the ignition switch and the functionality controlled by the OEM, normally-open relay. When the aftermarket system is in the disarmed state, the normally-closed relay is dormant in its closed position, thereby allowing the circuit to complete its intended loop. When the aftermarket security system is enabled, the normally-closed relay will open the current flow and prevent the current from reaching its target, thereby disrupting or disabling the operation of the vehicle function. If the normally-closed relay fails, it fails in its closed position, thereby not affecting the OEM system.