[Summary] No smoking sign

Exact usage of the “chime” switch varies by operator as far as how and when it’s used and what it’s supposed to communicate to the cabin crew at various stages of the flight. It also doubles as a memory device for the flight deck since it doesn’t do anything except make the “ding” noise.

Generally speaking (again, operator specific) the pilots will flip the switch to off when the cabin crew have reported the cabin is secure for pushback, then back to on at some point during taxi when the cabin crew report cabin is ready for departure. They’ll then flip it off when they want to signal to the cabin crew that they can leave their seats. If for some reason no signal is given, they’ll be released when the seatbelt signs turn off. Then they’ll flip it on again when the cabin is ready for landing.

Well ok, if the switch doesn’t do anything other than make a noise, how is it useful for the flight deck? Notifications, as far as if the cabin is secure for whatever stage of flight, can come at any time. Rather than getting to a cabin notification item on a checklist and having to recall if you did receive cabin secured from the cabin crew, you can look up and see what the no smoking switch is toggled to and check it verse where it should be. For example, in my scenario above, if you’re on the before takeoff checklist and the switch is off, then you know you have not received word that the cabin is ready for departure.

There’s this other topic here on IFC where other users describe different usage of the no smoking sign switch, as well as some automated chimes on some Airbus aircraft it seems if you fancy a read.