Abstract: A padlock includes a body and one or both ends of a shackle can be locked within the body by a lock bolt operated by a locking mechanism, such as a key-operated tumbler. The shackle contains an internal electrically conductive element which is connected in an electrical circuit with a battery and an alarm, both of which are located within the lock body. In addition, a series of insulated wires can be positioned along the inner wall of the body and are also connected in an electrical circuit. If the shackle or lock body is cut, or if the shackle is pried or separated from the lock body, the electrical circuit will be closed to actuate the alarm. The circuit is arranged so that either no power or minimum power is drawn from the battery unless the security of the padlock is violated.