Well, actually, that's untrue. Carbonylhemoglobin formation due to metabolic and environmental CO, and subsequent breakdown releases CO. There are, in fact, CO

Well, actually, that's untrue. Carbonylhemoglobin formation due to metabolic and environmental CO, and subsequent breakdown releases CO. There are, in fact, CO breath analyzers. Smokers and smoke inhalation patients have much higher levels, whereas ordinary healthy people have detectable, nonzero levels. For the point of detecting crowds, it's still meaningless.