Solved: Nest Protect Keeps Beeping Twice After Replacing Batteries & Doing Health Checkup

[DadCowie]

Moderator edit: Subject updated for clarity and findability.

I have three 2nd Generation Wired Nest Protects (all purchased new in September 2022) and this afternoon, one of the units started beeping twice every 60 seconds. I replaced the existing batteries with a new set of Energizer Lithium AAs and it is still beeping. I opened the Nest app and checked the status of the unit there and everything is showing OK, yet the beeping is still happening. Surely this unit isn't due to be replaced after 14 months as the technical info shows "Replace by January 23, 2032"?!  Please help as the beeping is now going on six hours!

[DadCowie · Accepted solution]

Figured it out.  Unbelievable coincidence that there was a separate CO monitor tucked away that we had forgotten about and it was chirping as a warning that it needed to be replaced!