@Clara116 and @Mike-And-Jane0 From what I researched, those who live in all-electric homes should have them installed because CO can seep into the house form an attached garage, cars on the street ( those living in densely populated urban areas) emitting into homes having windows open, use of a generator in emergencies, like a power outage.
I have them as I still use gas for my heat, hot water heaters and of course my stove.
Clara, you sentiment is right on that it is better to be safe than sorry. And yes, we all have to apply by the rules of AirBnB to the lowest level of host understandings that have been set. We at times might find them redundant or obvious.
When I was working in medicine, if it wasn't documented it wasn't done plus our ever loving SOP's, Standard Operating Procedures and Algorithms were written, and yes, sometimes pictures included, to provide to the lowest level of comprehension of who might be reading in mind. It is not fair to have anyone assume that I or anyone knows all or every step of a procedure.
Enjoyable Holidays to all,
Bettye