This musical wireless doorbell chime is easy to install, with no electrical wiring and no expensive through-the-wall drilling. Installation is as easy as mounting the button on the exterior of the door and plugging the receiver unit into any indoor electrical outlet. To extend coverage to more rooms, just purchase additional receiver units that can be plugged into any room within 250' of the transmitter. You can distinguish between front and back doors by adding more transmitters and programming a different tune on each. There are thirteen 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. Unit is FCC certified. Two 3-volt lithium batteries for transmitter, included. STI-32500 FEATURES Wireless musical entrance chime. 32 individual privacy codes to protect against outside interference. Two 3-volt lithium batteries included. Operates up to 250 feet. FCC certified. Note: End user must verify the alarm and battery every six months and replace battery annually or as required.