This is a door/window contact that can be installed on doors, windows, and any other objects that open and close. the sensor transmits signal to the control panel when a magnet mounted near the sensor is moved away. External input for wired accessory is available at the N/C interface. the tamper protection ensures that sabotages attempts to move the contact will result in an alarm activation. LED flashes once: door/window is opened and transmitter sends signal to the control panel; LED lights on: low battery, please replace the battery immediately.