This is the digital, four-channel home intercom system that allows you to talk room to room. Unlike lesser models that transmit a signal through a home's electrical system and cannot reach rooms on different circuits, this unit uses a wireless 900MHz digital spread spectrum signal to transmit clear, uninterrupted sound to every room, up to 1,000', ensuring that all conversation is private and free of interference from other wireless devices in your house or the surrounding neighborhood. It is easy to set up due to a "learn" feature which links both units together into a private wireless network. Its voice activation mode allows you to monitor a room and you can conduct conferences using more than two units. Set of two. Requires four AA batteries that provide up to a year of operation. 1 3/4" H x 6" W x 3 1/2" D. (1 1/2 lbs.)