Surface Mount Magnetic Contacts Miniature size perfect for homes and offices Attractive cover keeps mounting screws and terminal screws hidden Standard gap: 3/4 in. 19mm Concealed or surface wiring Complete with spacers and mounting screws This protective device monitors the opening and closure of doors and windows. Alarm Contact switches are magnetic switches used to protect doors and windows for the most part. Doors are the most common place of entry and should be protected by your alarm system. The Home Security Store always recommends contacting every perimeter door in your home or business.