On Sunday, July 16, 2017 at 6:20:10 PM UTC-5, Frank wrote:

CO detectors have a finite lifetime and when battery goes detection
ability may be lost also. I replaced mine as well as old smoke
detectors a couple of years ago. I don't like having both type
detectors in one spot as if one starts beeping, you may not know which.


Yes, when the battery gets low they do have an annoying chirp to get
your attention.

It doesn't matter if both smoke and CO detectors are near each other,
if one goes off it's certainly going to get attention and I will be investigating what's causing the alarm.