Mains Powered Smoke Alarms all go off when power switched on

[Guest Neil T]

I have replaced the 9V batteries in 7 BRK mains with battery backup interlinked smoke alarms in a rental property I own (currently empty). I isolated the alarms from the mains using the breaker on the distribution board before removing each alarm and replacing the batteries. Once all the batteries had been replaced and alarms put back up, I switched the power back on. The alarms then all went off and did so for a perhaps a minute or more without stopping. In order to avoid alarming the neighbours and not knowing if they would stop or not I isolated the power again and the alarms stopped. Is this normal, or are they going off when connected to mains power because there is an issue.

 

Any advise would be greatly appreciated.

[green-foam]

I would suggest you "start again" and change the battery in one detector then switch the mains on, and repeat for each detector, it sounds like you have a battery / detector incompatibility  problem. This is the easiest non technical way to find out, although somewhat tedious, and also check the age of all smoke detectors, the life span is 10 years.