Abstract: A locking device for an electrical toggle switch has a fixed, one piece locking body. An opening extends through the body for receiving a mounting screw for a switch face plate to mount the body on the face plate. The mounting screw receiving opening is provided with an access in the body adjacent the opening to locate the mounting screw in the opening while the mounting screw is still engaged with the switch face plate. An additional opening extends through the body and is spaced from the mounting screw receiving opening. The additional opening is defined by an abutment for engaging the toggle arm of the switch and for preventing movement of the toggle arm from one position to another position, particularly from an off position to an on position.