I had trouble with them going off in humidity, they were past their expiry date so replacing them fixed the issue.

Did you open one up yet? That might give you a clue 🤔

E.g. I don't know exactly how wide the gaps are, but here it looks like small insects could get in. Maybe you have another problem than smoke 🫣

Are your smoke detectors linked to each other? Could be faulty wiring in the circuit, or a completely different smoke detector failing and sending out an alarm that triggers the others. The latter happened in my home when I was growing up: the living room smoke detector kept going off a few seconds before the rest of them would chime in, but it turned out it was the one in the nearest hallway that was failing and sending out bad signals. The living room detector was just the next in the circuit.

Depends on what kind of detector it is but alot of them use small amounts of radiation and a detector that triggers when the number of particles detected drops below some level.

How smoke detectors work

That being the case any particulate large enough to interrupt the particles could cause it to go off.

For example high humidity misty water from a shower wafting over a detector placed over the bathroom door, etc.

UPDATE: so they kept sending me the same model of smoke detectors so I didn't remove the old bracket, I would just mount the new detector in the old one. well, today, I see a moth larvae crawling out from behind it. I take the bracket off, and there we are; two moth nests. I think we've discovered the issue

Have you ruled out other types of fumes? Eg fresh paint, perfume, scented oil diffusers etc.

What country? AFAIK in the US you can't make the batteries replaceable. If they are wirelessly linked they can have auxiliary batteries for that, but (I believe) that's different than the main battery...

EDIT: I seem to be thinking of California, maybe not all of US.

Try replacing the batteries. That's often the reason for this type of thing.