We have a network of mains smoke alarms that have all been going off about every 10 minutes despite having their back up batteries replaced, cleaned etc . In the end we got an engineer in who said the thing to do was watch how many times in a minute the red light flashed and if it's very rapid then the alarm itself is faulty. We looked at them all over the house (10) and eventually saw the one that was flashing rapidly in the rear hall. He had to remove that one completely and it's cured it, they're not being triggered anymore. They were only fitted last year so weren't old so maybe yours is just doing the same thing ours was and needs replacing.Hope you get it sorted.