Product name: magnetic door switch. Some installation parts; Normally Closed: The magnet is almost conductive and open from the start.This is a set of magnetic sensing switches which are mainly used to protect doors and windows. A protective device monitors the opening and closing of doors and windows.Each size (LxWxH): approx. 106 x 38 x 10mm/4.2 x 1.5 x 0.4in; Detection distance: 50~70mm/1.9~2.7in.The wired part is usually installed on the fixed door frame, and the coupling part is mounted on the corresponding place on the door. < p>Easy to install and use. A good replacement for the old contacts. Easy to install with no hassle. High quality magnetic sensor contacts with strong magnetic response, sensitive and long life.