Hi, In our house we have 2 smoke alarms. One upstairs on the landing and one downstairs in the hallway. They've both been damaged by plasterers/dust, and so go off when they shouldn't. We've got a 1 year old, and waking up to a false alarm from the smoke alarm and a screaming baby isn't a fun time. I figured it should be easy to replace them. Went out, bought 2 wired smoke alarms. I came back, took the first alarm off and this is what I see: From the ceiling is: - Brown - Black - Grey - A yellow/green (earth) which doesn't attach to anything. The plug that went into the old alarm has: - Brown - Yellow - Blue They were matched like this: - Grey -> Blue - Black -> Yellow - Brown -> Brown. - Yellow/green -> nothing. The new smoke alarm comes with: upload image - Brown - Blue - White My assumption would be that this wants to be: - Brown -> Brown, just like it was. - Grey -> Blue, just like it was. - Black -> White... I'm not sure what this is but it's the only ones left. Before this was Black -> Yellow. I've yet to take the upstairs alarm off. I believe the black wire that used to go to yellow, but now perhaps to white, is for interconnecting the alarms - though I may be wrong. Just before I go with my assumption, I thought I'd better ask. It's difficult for us to get an electrician at the moment, and I really want to get the smoke alarms up - installing it is fine if I know which wires match which. Really appreciate any advice!