A lock includes a hollow lock body with a plurality of aligned first transverse holes, a cylindrical key plug rotatably disposed inside the lock body and having a plurality of second transverse holes aligned with the first transverse holes, and a plurality of tumbler pins extending into each set of aligned first and second transverse holes. The lock further includes a first control switch actuated by inserting a key into the key plug, a second control switch actuated by rotating the key plug relative to the lock body, and an electrical control circuitry including a first timer circuit connected to the second control switch, a second timer circuit connected to the first control switch, a warning device and an electromagnetic control unit both actuated by the second timer circuit. The first timer circuit disables the second timer circuit for a predetermined time period when the first timer circuit is actuated. The warning device sends out alarm signals and the electromagnetic control unit prevents the rotation of the key plug for a predetermined period of time if the lock has not been opened after the second timer circuit has counted down a preset time period.