most carbon monoxide detecter uses a platinum oxide metal.
it reacts with carbon monoxide and releases energy:
PtO + CO--> CO2 + Pt + heat
the detector measuere how much the temperature has changed and sound an alert when necessary.
the Pt regenerates itself in the presents of air:
2Pt + O2 --> 2PtO
there are also some other carbon monoxide detecter, you might wanna check the website out:
http://www.city.greatersudbury.on.ca...&parID=980
ps: remember: "When you smell an odorless gas, it is probably carbon monoxide"