Good point. I should check the codes. Some line powered CO monitors are battery-backed, but that's just for brief outages (not the kind you get your kerosene heater out for). What I really would like is 12 or 24Vdc powered fire/smoke/CO/security monitoring system that runs off batteries charged from wind/solar. Maybe with some auxiliary lighting that would come on if it were dark AND the power was out. It's not so much that I NEED something like that, it's more like something to tinker with.