"Vass" wrote
Carbon Monoxide poisoning

these alarms you can buy appear to hang from the ceiling
as I understand it, carbon monoxide is heavier than air so surely would
sit on the ground
i.e. bit late if the gas reaches the ceiling
am I barking mad or have a point here?

See: http://www.newton.dep.anl.gov/askasc.../chem03364.htm

Steve S