Physen&reg; Model Piano Key Design FXA2t1 Wireless Doorbell Kit of 2 Transmitters & 1 Receiver Housing: Piano key appearance looks very modern & stylish. Made of high quality ABS environmental protection materials with anti-burn and impact resistance. 52 elegant music for your choice. They are very melodious. Operating range of over 500 feet (1000 feet in open area). 4 levels of adjustable volume from 25db to 110db. Sound is loud enough. Receiver: easy plug-in design(Please DO NOT plug receiver into UPS units); Transmitter : Powered by 23A 12V Alkaline battery( Battery Included) Easy installation: No wiring required to install the product. Just plug the receiver in the wall, and mount the wireless transmitter using the supplied double sided tape or mounting screws. The door chime units can be configured to ring with different melodies/ringtones. It can not only tell you someone knocks at your door, but also be used to look after your little kids or aged parents.