Two to one front and back door function Wireless digital doorbell (DC) 1. Differente tones for front and back door,let you recognize easily. 2. Pager function is available. One transmitter can be fixed at head of bed for the special people. The other transmitter can be used for doorbell at the same time. 3.100 meters range in the open air. DIY fashional design. No wire needed and easy installation. 4. Digital design, no interference from neighbours or others.