A smoke detector is there to alert the occupants of the building so that they get out. If it was an actual alarm system that is connected to a dispatcher, the firefighters would've been notified.
Yeah, as originally designed perhaps, but what if you could add a bit of tech to make sure your pets are safe? Or you're not coming home only to inhale carbon monoxide? I don't think $99 is a ridiculous expense for such peace of mind, even if it's not proven to be full proof just yet.
Because CO kills surprisingly quickly -- unless your commute is in the order of a couple of minutes you'd be too late. Also you don't send a person into a house with a CO leak so asking you neighbour to retrieve your cat would be placing them in danger.
My point is that the smoke alarm and the CO alarm should be exactly what they are simple alarms that allow occupants to escape in an emergency. Adding IOT capabilities doesn't add to the alarm functionality in sensible ways. However, it does risk introducing vulnerabilities. I don't want my smoke alarm to start sending spam emails (this really happened with a smart fridge a couple of years ago).
You're being awfully pedantic. Have the neighbor shut your gas off. Have your landlord alert the neighbors. What if you just left for work? I can find a bunch of scenarios where the information can be useful, whereas you seem determined to argue that only the occupants (who might just be kids burning toast) should have this information.
The information is intended to allow the occupants to escape safely if required. In the case of a CO alarm no one should enter the premises until qualified engineers have made it safe. The the case of a smoke alarm the occupants are the only ones that can safely decide if it is a false alarm -- if there is a fire no one should enter the premises until the fire has been dealt with by qualified personal. What you are suggesting would mean adding a general purpose computer to essential safety equipment. Anything that adds complications and could affect the main function of the safety equipment would need to be considered very carefully.