Linked Mains Smoke Detectors

I have three smoke detectors from Screwfix (product 19792 MAINS SMOKE ALAM PHOTO OPTICAL) all linked together.
They worked fine for 6 months - then they would just randomly go off and sound for about 15 seconds
I don't think you can tell which one triggers the alarm, but I disconnected one - and left it for a few weeks - nothing happened so I assumed it was faulty and brought another one.
Two weeks later and the middle of the night the alarm goes off for about 10 seconds
Then another few days pass and they go off again
Anyone had similar problems? Anyone know how to fix them? Where should I start looking / how can I diagnose what the problem is with these?
Mark
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Disconnect the linking feature for a while and see which one goes off.
Christian.
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Sorry if this is an obvious q`s but have you checked and repaced the batteries, cos flat bats can sometimes cause this...
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The Question Asker wrote:

I guess you also have the answer to the US power cuts as well.
They took the batteries out of the grid!!
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