The IEH-1C2D audio handset sub master station is for use with the IE2A2DU master stations; max of two per system. Two and Four tone electronic chime. Chime volume adjustment on handsets. Answer the door from any room station. All Call internal calling between handsets. Door release button (additional hardware required). AC or DC power source ( 12-16V AC or 12-24V DC ). Wiring::- 2 non polarized to door station, plus 2 to door release. and 6 wires in loop between rooms Distance 150 mtrs. ( 0.65mm - 22AWG), 360mtrs ( 1.0mm ). Size: 100 x 210 x 68mm ( WHD).