Carbon monoxide is lighter than oxygen and carbon dioxide, about the same as nitrogen. All things being equal it will slowly rise in a room. The reason carbon

Carbon monoxide is lighter than oxygen and carbon dioxide, about the same as nitrogen. All things being equal it will slowly rise in a room. The reason carbon monoxide is a threat in the lower levels of your house is not because it sinks but because that's where your furnace and hot water heater are. Combined smoke and CO detectors are fine (and there are many on the market today).