Used to do a two-day charity bike ride. We’d rent a large house to sleep everyone. Not on my floor, so I slept thru it but one of the detectors had the low battery beep-once-a-minute in the middle of the night. However, for whatever reason, it was not on the ceiling; maybe it was a CO detector? We were dying laughing at my one, quite-exhausted teammate the next morning with his tale of trying to echo-locate this thing that only beeps infrequently in the middle of the night & how he was getting madder & more frustrated with each single beep.
Each year we have a massive Disaster Recovery exercise involving about 30 people on a 3 day WebEx meeting. Last year one of the vendor’s technicians was clearly working from home and had a smoke alarm chirping in the background. Everyone in the meeting noticed it, but she didn’t even hear it any more. I actually included a line in the post-mortem notes that technician X needed to change her smoke detector batteries for the next test. The vendor was pretty embarrassed.
Also, if you have an attached garage with a regular (not EV) car. If your car is running in the garage, especially if the door is closed, CO can make it’s way into your living space.
And devices (levers, pull-rods, buttons, whatever) that a human in the space can manually activate. Which is often done by mischievous students.
As a side comment.
Fire alarms are often activated by breaking a glass cover over a button. My sister-in-law had a job, working at home for a while, scratching a line on the glass so it would break cleanly. Once the glass is broken, the button pops out.