I have the distinct impression that there is a bizarre legal/regulatory problem with this: safety devices need to comply with local regulations, even when those regulations are inconsistent or weaken safety. For instance, in the US, a UL-listed CO detector must not alert at problematic-but-not-immediately-dangerous levels. So you end up with absurd hacks like this:

https://www.kidde.com/home-safety/en/us/products/fire-safety...

That’s a real name brand device that is not a CO detector because it does not meet the UL requirements.

I can easily see AirBnB not wanting to get involved.

(Also, there are properties listed in multiple services, and maybe the owners/managers don’t want to put in special gadgets for each service. And maybe people who rent their own home and live in it some of the time don’t want the AirBnB cloud intruding.)

For starters, the place you're supposed to install your CO2 detector is not the same place where you're supposed to install a CO detector.

Hardware is doubly hard when you are as international as AirBnB. Wifi has to conform to local regs with regard to channels and tx power. I wouldn't be surprised if there were varying local regs for CO detectors, too.

I mean plenty of companies do offer these things, so likely you’d just subcontract out to them. And it’s not like you need to offer everything everywhere all at once.