Abstract: An accessory for use with a vehicle, equipped with a vehicle anti-theft system, and an interrogator device for the anti-theft system. The accessory includes a connector arrangement for establishing between the vehicle anti-theft system and the interrogator device an electrical current carrying path which passes through the vehicle ignition lock cylinder mechanism. An ignition key arrangement is provided which is cooperable with the connected arrangement and permits mechanical operation of the vehicle ignition switch mechanism while the electrical current carrying path remains established.