I have 7 smoke detectors hard wired together, and I put in new batteries a
few months ago. Just today I started to get a "chirp" about once a minute.

I have a question..... if one battery is dead, do they all chirp? Or only
the one that is dead? I hate to run out and buy 7 batteries.

I swear they are ALL chirping, but they are throughout the whole house, so
it's hard to tell.