This product has the national standard, European standard, American standard, British standard Special instructions: 1, AC doorbell, receiver (indoor unit) using household power, plug directly into the socket can be, do not cost the battery, environmental protection and convenient Transmitter (outdoor unit) using a battery for about a year 2Super strong reception Suitable for home, office, hotel, buildings, dormitories, factories, construction sites, etc. 3, a range of use of the same doorbell, will not interfere with each other Wireless high-frequency transmission technology, the same frequency code, effectively avoiding the neighbourhood of mutual interference and false alarms brought about by the trouble. Warm reminder: this product is empty without obstacles straight line remote control distance by strict testing is not less than 300 metres. Can meet the needs of different family environments, the general family across the security door and several walls is no problem. Features a: anti-interference will not appear crosstalk. Features two: receiver intelligent flashing lights Features three: long-distance wireless receiving signal. Feature 4: Adjustable volume and music installation is simple and easy to use (default ding dong ding dong) 3 adjustable volume 38 music to choose from