faulty smoke alarm

Might be worth a try - clean the dust and dead flies out of them. If that doesn't work, you could try disconnecting each one in turn to find which if any sensor is faulty. I that doesn't work then the problem is probably central and may be beyond diy.

You have of course ruled out smoke or steam (eg from a kitchen or bathroom) or electrical interference? The Kidde ones I fitted 18 months ago had surprisingly stringent requirements relating to distance from nearest bathroom, distance from nearest light fitting etc.

If it's a fault then chances are it is just one of the three units. Disconnect one by one and leave each for a couple of days to identify.

I can understand 1 going off,but all 3? sounds like something common to all three, mains tripping them? As advised disconnect all but one and do each the same in turn.

The clue *might* be in the phrase "linked" :-P

Yeah..managed to set all mine off yesterday doing some plumbing..flux smoke gets them really excited..