What are recessed door sensors?

Recessed door sensors are used in security systems to see if a door is open or closed. Most door sensors are surface mounted, meaning a small contact or sensor mounts on the door frame and a magnet mounts on the door itself, right next to the sensor. When the door opens the magnet is removed from the sensor, breaking the connection and causing an alarm. A recessed door sensor works the same way, however the contact and the magnet are hidden or recessed into the door and door frame. A small, usually circular hole is drilled into the door frame and in a corresponding point on the door itself. The sensor and magnet are then recessed into the holes, hiding them entirely from your field of view. Recessed door sensors are ideal for homes or businesses where you are very sensitive to the décor, and it would not be acceptable to see any part of the security device mounted on the door itself. Do note, that wireless recessed contacts or door sensors do have a slightly diminished wireless range due to their small size and additional interference from being inside of a door or door frame.