OldShooter
Give me a museum and I'll fill it. (Picasso) Give me a forum ...
My funny story. We started hearing a cricket chirping in the basement. Try as I might, I could not find that cricket and my hearing could not exactly localize the sound. So I attacked with insect killer. Two full cans spraying joists, subfloor, etc. No joy.3 more beeps just now. so about 12 hours apart. These sounded farther away to me but then the furnace is running and might muffle it.
You would think they could invent something. I called the company and they said the bad one be flashing red. No red here.
Now I understand why people disable these things! Of course I am not 100% sure what it is.
Finally found the cause: A small motion detector alarm that we had bought to keep the dog from going somewhere he didn't belong. It hadn't worked very well for that so it ended up on a shelf in my workshop. It took months, maybe a year before the battery got to the point where the "cricket" alarm began.
From that, my guess is that the noise is coming from something besides the smoke detector(s). Some little electronic gadget that you have forgotten about. I have an app on my phone called "Sound Meter" that shows the average volume of sound it hears. Maybe something like that could be used to localize the emitter, though if it only beeps every 12 hours chasing it could take some time.