Magnetic contacts are detectors which are installed on doors and windows. They can be thought of as a type of magnetic switch. When a door or window is opened, a switch is triggered and this in turn signals the alarm to turn on. There are two types of magnetic contacts: surface and recessed. Surface contacts are installed on the window or door frame itself while recessed contacts are embedded unto the door or window. The clear difference is that surface contacts are easier to install than recessed ones but have the disadvantage that they are easily seen.