I have two smoke detectors chirping in the basement.
I changed the batteries in all the smoke detectors that I know about.
I still have two smoke detectors chirping. Probably in a tub with a bunch of other items.
The chirping will become more frequent and I will find them, if Mrs ERJ does not strangle me first. The other possibility is that the batteries will eventually die.
It is a good life when my biggest problem is a couple of "extra" smoke detectors that want attention.