Abstract: A device, mounted on an automobile, operative--upon being pre-set to a working position--to produce an exteriorly audible signal if the automobile is subsequently operated without authority, as for example when stolen. The device comprises, essentially, a frame-mounted post unit having a wheel on its lower end, the post unit being vertically adjustable from within the automobile between a normally raised, out-of-use position wherein the wheel is clear of the road, and a lowered, working position wherein the wheel is in contact with and rotated by the road upon travel of the automobile, and a signal unit associated with the wheel and functioning upon rotation thereof to produce such audible signal, apprising others--such as law enforcement officers--that the automobile is being operated without authority.