@Ben-and-Sam0 They aren't required, so I don't know what you mean by Airbnb not making an exception. It's as absurd to require or install one if it's not necessary as it would be to put up baby gates if you don't have babies or children and don't accept them in your listing.
@Brian-and-Tosha0 I also have no source of CO in my listing and no CO detector. I mentioned why under "other things to note". Whether all guests read that or not, I don't know. I've certainly never had a guest express any concern about it.
It's very irritating and unfair how Airbnb put that under our amenities with a big black line across it, as if we are somehow negligent hosts who don't care about safety.