Fort Smart Door and Window Contact Sensor for Smart Home Alarm System. This sensor detects changes between a transmitter and magnet to alert you when a window or door has been tampered with. Attach the sensor to the side of a door or window frame using the mounting screws, wall plugs and magnet spacers provided, even on recessed doors/windows. Each sensor is battery powered (batteries included) meaning they can be placed in a room of your choice and away from an active power source. With the click of a button, each sensor connects to the Smart Alarm Hub (sold separately) via radio frequency, from a distance of up to 80m (clear field of view).