The DB-1MD is an audio only master for the DB series hands-free two-wire door system. This system will support 1 door station with 1, 2 or 4 buttons and up to 5 inside stations per button. The DB-1MD hands-free master features a call tone volume control with mute indicator, receive volume control, All Call button, Talk button, and Off button. It connects via 2 wires to the DA series door station. Up to 4 sub stations can be added to this master and communication is possible between the 5 total stations via the All Call button.