"CO detectors can be placed near the ceiling or near the floor because CO is very close to the same density as air" per http://en.wikipedia.org/wiki/Carbon_mono

"CO detectors can be placed near the ceiling or near the floor because CO is very close to the same density as air" per http://en.wikipedia.org/wiki/Carbon_monoxide_detector http://en.wikipedia.org/wiki/Carbon_monoxide_detector