This is a SONOFF DW2 RF 433MHZ Wireless Door/Window Sensor which triggers the transmitter by separating the magnet from the transmitter, then the transmitter will send an alarm message and pushes it to the app .it is used to trigger alert messages when the door/window is opened and closed. With this intelligent wireless magnetic door detector of separation by triggering, mainly opening of door and window and any other devices can be opened and closed and Make reports for devices out of close and low battery.