Abstract: A security device for movable objects such as a bicycle includes a lock box that is attached to the movable object, a locking chain that physically secures the lock box and movable object to an immovable object such as a bike rack, and an electric alarm circuit. The alarm circuit is armed by a lock switch that closes the lock box and is set off by severing of the cable, which is an integral part of the alarm circuit. Alternatively, the cable and lock box include an optical conduction path which is sensitive to tampering and difficult to bypass.