It is a unique wireless doorbell, the differences between other plug-in doorbells is the push button self-generating launcher, no battery or wire needed, it can provided itself the power after pushed; It can reach up to around 200m in the open air, the push button transmitter is IP44 waterproof, acceptable to use outdoor; Musical doorbell, with selection of 58 melodies, 4 level volumes to turn up/down; LED indicator, you can add launchers or receivers for your need, it can be heared from any rooms rather than miss the visit; Easy install, no wire needed, no worry about screwing up the wall, stick the launcher bell outdoor and plug in the receiver indoor,(double-sided tape included) then it starts to work for your home convenience and security; Specification: Material: Plastic Size: Outdoor Device:Approx. 82x46x21mm/3.22x1.81x0.83inch Indoor Device:Approx. 95x65x24mm/3.74x2.55x0.95inch Working Distance: 200m Voltage: 110V Plug: US Package Includes: 1 Set Wireless Doorbell