The Honeywell 947-75 is a 3/4” diameter steel door recessed contact designed to protect steel doors from intrusion. You will need to wire your 947-75 recessed contact back to an open wired zone on your alarm control panel. You will need to splice the wire leads coming out of the backside of the 947-75 recessed contact to the contact loop wire coming from your alarm control panel. Most people prefer recessed contacts to surface mount contacts as they provide a cleaner look. While surface mount contacts distract from the decor of your property, recessed contacts are hidden within your door and window frames and are therefore much less obtrusive. Unfortunately, as recessed contacts need to be drilled into a door or window, they are typically smaller devices. When you install a small magnet inside a steel door, the magnetic field normally gets obstructed and the contact does not work. However, the 947-75 uses a much larger magnet which is able to penetrate the steel door and energize the recessed contact. The steel door recessed contact is ideal for commercial and industrial applications. The Honeywell steel door recessed contact has an internal reed switch with a rating of 100mA at 28VDC. The reed switch is a Form A, SPST, normally closed contact that can be wired to any normally closed zone. When the corresponding magnet is in close proximity to the contact, the contact loop is closed and the alarm control panel is happy. If the steel door opens while the system is armed, the magnet separates from the contact and the loop opens causing an alarm. The magnet spacing gap of the 947-75 recessed contact is 1/2” when installed within a steel door.