The Xiaomi Aqara smart window / door sensor can detect the opening and closing of doors and windows and send a message to your phone via the App. It also has the ability to match with other matching Xiaomi smart devices such as the gateway remote control, smart lamp and air filter. This sensor can help you to create your own smart home. The window / door sensor consists of a sensor and a magnet. It detects the opening and closing of doors and windows by detecting the proximity and separation of the sensor subject and the magnet.