Ahh, the if it just saves one life reasoning. A slippery slope, my friend, when you consider the intent of those behind pushing these types of laws- it's almost always nanny-state liberals. I don't agree that we should be going further down the slope of governing and passing laws to dumbest common denominator that also stick the majority with having to bear the cost and hassle because of their stupidity.
If you own a house it's your responsibility to know what is going on with it and to maintain it. If you have a fossil fuel burning appliance you need to check on it from time-to-time as they are the source of potentially emitting CO into a house. Don't know what you're looking at then hire someone that does(furnace mfg's recommend yearly service). Aside from dummies that run their gasoline generators or fire up their charcoal grill in the house, every single case of CO poisoning I'm aware of is because of poor maintenance causing a dirty burning flame that could have been addressed by cleaning the burner and adjusting it properly.
That also begs the question, if we're gonna have gov't step in to save people from their own stupidity, why not go straight to the source and dictate people have their appliances cleaned and serviced annually? Can't the nanny-staters get anything right? Who cares what it costs, or the hassle, or the intrusion- we're talking lives here, and doing that will save far more than a wimpy CO detector.