... repast enviroment.FeaturesWireless Call BellSend call signals without wiresCompatible with all main unitsWork with GDH100, GDH400, GDH500, GDH300Long Life of BatteryOne ... 67(D)*28(H) (mm)Weight 36.5g (With battery)Control Single call buttonOutput Power 10mWFrequency Band 315MHzModulations ASK ... 95% relativehumidity for 4 hours wireless restaurant waiter call system, high quality and good service