Abstract: An automotive anti-theft device is operatively arranged to interrupt a vehicle's starter circuit until the key-operated ignition selector switch has been physically rotated to the "start" position. The anti-theft device includes a mechanical device adapted to convert rotational movement of the selector switch into linear motion, a hydraulic piston arranged to convert such linear motion into a flow of hydraulic fluid, and a pressure responsive device mounted on the vehicle's starter. The pressure responsive device has a movable member operatively arranged to move in response to such flow of hydraulic fluid, and is adapted to complete the starter circuit between two terminals thereof only when the selector switch has been rotated to the "start" position.