Connection"Do not disturb" and "Make up room", DC 24 V Hotel switch room unit 2 with hotel push-button corridor unit with bell 3 and optional relay 1.Hotel switch room unit 1 and hotel centre plate corridor unit without bell 2."Do not disturb" and "Make up room", AC 230 V~Hotel switch room unit 2 with hotel push-button corridor unit with bell 3 and optional relay 1.Hotel switch room unit 1 and hotel centre plate corridor unit without bell 2.