According to http://en.wikipedia.org/wiki/Carbon_monoxide_detector
"This is a type of fuel cell that instead of being designed to produce
power, is designed to produce a current that is precisely related to the
amount of the target gas (in this case carbon monoxide) in the atmosphere.
Measurement of the current gives a measure of the concentration of carbon
monoxide in the atmosphere. Essentially the electrochemical cell consists of
a container, 2 electrodes, connection wires and an electrolyte - typically
sulfuric acid. Carbon monoxide is oxidized at one electrode to carbon
dioxide while oxygen is consumed at the other electrode. For carbon monoxide
detection, the electrochemical cell has advantages over other technologies
in that it has a highly accurate and linear output to carbon monoxide
concentration, requires minimal power as it is operated at room temperature,
and has a long lifetime (typically commercial available cells now have
lifetimes of 5 years or greater)."
My concern is that non of these sensors (both seminconductor or
Electrochemical) seem to be sensitive enough to measure street level CO
(0<8ppm).
Very interesting. Thanks.