Abstract: A multi-purpose alarm system is designed to produce an alarm signal in response to the movement of an object relative to a fixed position, such as occurs when doors, gates or windows are opened, or when vehicles are moved. The system operates with an emitter providing a beam of light (such as a laser beam of light) mounted in a fixed location. A mirror or retroreflector is mounted on a movable object to intercept the beam of light and reflect it back to a detector located adjacent the emitter. The detector activates an alarm whenever the movable object is moved a sufficient distance to prevent the mirror or retroreflector from returning the beam of light to the detector. Interruption of the beam of light in its path to the mirror or retroreflector is not required to activate the alarm; although the alarm also is activated in the event of interruption of the beam of light from the emitter.