Smoke alarm - 3 beeps

I bought a set of three smoke alarms a year ago. Now, one of them gives 3 beeps every half an hour.

I deleted the alarm from the app and performed a reconfigure. No solution.

This could be due to a dirty sensor I found out, but that is not the case. The battery is guaranteed voor 10 years and the apps shows no problem with the battery.

The only conclusion is that the smoke alarm has some kind of defect?

Or is there any other solution?