Abstract: The alarm mechanism is electrically operated and includes an electrical switch having an arm which projects beyond the alarm's housing. The arm is semi-rigid and flexible such that it may be engaged to actuate the switch yet will deflect to one side to permit passage of a door engaged therewith during opening. The housing is mounted on a wall immediately adjacent to the door with the arm extending along side the door. Upon opening the door, the arm is engaged thereby sounding the alarm. The housing is frictionally and rotationally mounted on the wall such that it may be swung to a position in which the arm is moved out of interfering or engageable relation with the door.