The Interphone F5 from Cellular Line is the first Bluetooth Intercom to be released with advanced intercom features. Up to 6 F5's can be connected to extend intercom range to up to a mile. The frustration of hearing mysterious beep tones has been eliminated with the Text to Speech (TTS) feature of the F5. TTS gives audible voice indications when the intercom connects, disconnects, music plays or pauses, and when a phone call is incoming. The F5 TTS feature will also tell you who is calling so you can avoid answering the call if desired. Bluetooth 3.0 technology gives the F5 the longest battery life of any Bluetooth intercom to date.