The Portable Plus Wireless Door Chime and Bell Push from Honeywell is a great solution for homes that don't have a pre-wired doorbell for the front entrance. It will also work well with apartments, travel trailers, back entrances, garages, dorm rooms and offices. The bell push unit communicates with the chime module via radio frequency (RF), and each are powered by battery, so no wires or professional installation is required. There are four different chime sounds available with an adjustable volume setting. A blue LED visual indicator has been built in to the chime module which helps those that are hard of hearing. The chime sound and LED light can operate together or independent of each other. The chime module is free standing so you can take it wherever you go in the house up to 150 feet away from the bell push module. The bell push module is rated for outdoor use and has a UV resistant plastic housing with a rainproof push button. It can be mounted with included screws or double-sided tape. The modules have been individually coded to prevent interference with other transmitters such as PIR movement detectors and telephone ring detectors. The bell push module is powered by an included CR-2032 lithium battery, the chime module is powered by three Alkaline C batteries, sold separately.Pre-Loaded Chimes Ding Dong 4 Note Modern 8 Note Westminster Saxophone RF Interference Dense walls and metal can reduce range by the following approximate amounts: Dry-lined partition wall: 10 - 30% Single-layer brick wall: 20 - 40% Double-layer brick wall: 30 - 70% Metal panel/radiator: 90 - 100%