Bird
Rest in Peace
Since the CO results from a fire or combustion of some kind, I'm sure that many homes now would not have a furnace going if the electric power is off. But if you have a wood burning stove or fireplace, or a gas burner not controlled by electricity, or as in our RVs, the furnace was controlled by electricity alright, but it was the 12 volt battery power. And of course internal combustion engines running, whether cars, lawnmowers, or others would generate CO without electric power being on.
Some years ago one of my aunts, living in a Dallas suburb, phoned her sister (another aunt) in Dallas, one Monday morning. The one in Dallas answered but the conversation made no sense, so the one in the suburbs, and her husband, drove into Dallas and found the aunt in Dallas, and her husband, barely conscious. They were sent to the hospital via ambulance and the fire department found some insulation had fallen over the vent for the gas furnace in the house. The aunt and uncle thought they had just taken a brief nap on Saturday and didn't realize they'd been out more than 48 hours. A slightly higher concentration of CO and they'd have both been dead.
Of course, I've personally had some experience with suicides by CO with car engines left running on purpose to produce the CO. I don't recommend suicide, but I do belief if a person were going to do it, that's got to be the best way I've seen.