Abstract: A security system, particularly for a vehicle, comprises an electrical security key usable to make circuits which either directly, or through relays controlling other circuits, render operable electrical devices necessary for the starting of the engine of the vehicle by a conventional ignition key and switch. To confuse a person attempting to breach the security, conductors necessary to supply power to the devices are made discontinous within a wiring loom of the vehicle and other conductors are tapped-in at sides of the discontinuities and extend to relay contacts operable by the use of the key. Further to confuse such person, further conductors are connected to other relay contacts but have no operating function.