The Byron IB Series 2 way audio door intercom has a outdoor unit complete with a mounting bracket and lit bell push with name plate. it has an indoor unit with handset and button for door lock function (door lock part code DB5005). Supplied with 10 metres of cable that can be extended up to a maximum of 30 metres. In addition, the intercom provides support for up to 2 monitors per button (part number BYRIB60). IB61: Audio Intercom for 1 Apartment.IB62: Audio Intercom for 2 Apartments.IB63: Audio Intercom for 3 Apartments.IB64: Audio Intercom for 4 Apartments.IB60: Additional Handset.The Byron BYRIB62 Audio Door Intercom is ideal for 2 apartments.