Abstract: A lock-activated cut-off switch for use in connection with electrically operated overhead garage or roll-up warehouse doors. The switch of the present invention takes the form of a spring-biased, counter-weighted, wedge-shaped, trap door or gate disposed to close against the switch frame having an opening which is lined up with the opening constructed to receive the lock bolt or bar when the lock is actuated. A pair of conducting wires which respectively terminate on contacts at the lower end of the frame on opposite sides of the opening are electrically connected through contacts and a conductor on the trap door or gate, when the gate is closed, and are instantly disconnected when the trap door or gate is opened by actuation of the lock bar or bolt. This breaks the circuit to the electrically controlled operator disabling the mechanism for opening and closing the garage doors.