Abstract: An alarm system for detecting and signaling the unauthorized opening of a movable closure, includes a support plate, a toothed rack, slidably supported on the support plate, a gear, rotatably mounted on the support plate and, in mesh with the teeth of the rack, spring means and a level arm coupled to the gear, and a bell mounted on the support plate. The alarm system is self-powered and is mechanically actuated by opening of the closure. The system is reset automatically by closing the movable closure.