The STI Wireless Chime Kit is a wireless doorbell. The button mounts on your wall outside. The receiver plugs into a standard power outlet inside. When a visitor presses the button, the receiver chimes. To hear the doorbell in multiple rooms, simply add receivers (additional sold separately). You can distinguish between front and back doors by adding more transmitters and programming a different tune on each. There are 13 sounds that can be selected with the push of a button on each transmitter. For security, there are 32 individual codes to protect against outside interference. Receiver works up to 250 feet away from transmitter. Volume adjustment: low, medium, high. 13 selectable doorbell chimes: Ding, Ding Dong, Westminster Chime, Star Spangled Banner, Hail! Hail! The Gang's All Here, Jingle Bells, Auld Lang Syne, Dixie, The Yellow Rose of Texas, Happy Birthday, Beethoven's 5th, Joy To The World, Take Me Out To The Ballgame. CONTENTS: Chime Button (transmitter), Chime Receiver, (2) 3 volt lithium batteries (installed), Double-sided tape, Screws.