Features:  
Easy installation - no wiring required
Weatherproof on Transmitter
RF transmission up to a distance of 100M
Adjustable Volume Control
8 selectable channels minimize interference & false ringing
The transmitter is supplied with a mounting bracket for easy installation on the door frame
Runs on 3 x "AA" size 1.5V alkaline batteries(Receiver)
Runs on 3 units CR2025 lithium button cell batteries or 6 units SR 41 button cell batteries (Transmitter)