Abstract: A self-contained alarm system mounted in a housing is adapted to be mounted between the clamps of an outboard motor and the transom of a boat. The clamps of the outboard motor are electrically coupled to circuit means in the housing of the alarm system through electrically conductive sensor members in the housing. The circuit means acts as a discontinuity or open circuit detector. When a clamp of the outboard motor is backed off, either intentionally or accidentally, the circuit means electrically detects the change of resistance and activates a sound device located in the housing.