Safety Technology International, Inc. STI-3551 Additional Wireless Entry Alert Transmitter – This additional wireless transmitter and magnet is easy to install and notifies when protected door is opened. Chime sounds when transmitter and magnet are separated. It greets visitors, customers or clients with the sound of music and alerts of their once the connection is separated. Operates up to 500 feet (line of sight). Uses 1 AAA battery Included. There are ten selectable sounds (with the push of a button) on transmitter. Note: End user must verify the alarm and battery function every six months and replace battery annually or as required. STI "We protect the things that protect you."