... in two sides. super door contact MC004 wireless door contact door sensor The common door cotact battery lifetime is over ... Be honest, it is so hard to get this door cotact battery , cuz it is a little special ... relative humidity ≤90%low bat voltage function this door contact is suitable for our 2200,2300,2300G, ... when it is the low bat battery, this door contact will send this signal to our host machine ...