The alarm can collect more than 2 alarms to a online system through LEARN key(LEARN). All alarms in the system will give an alarm when one of them detected the signal. The appearance of it is very nice. It"s safe and convenient to install, can be installed on wall or ceiling. It"s widely used in house, shop, restaurant, storage, engine rooms, entertainment locations etc. TECHNICAL REFERENCE Working frequency: 868. 35MHz Working temperature: -10 ~ +40C Alarm volume: 85dB/3m