How do electric carbon monoxide detectors work?
There are three major types of carbon monoxide senors.


Biomimetic: A gel changes color when it absorbs carbon
monoxide.
Metal oxide semiconductor: When the chip's circuit detects
carbon monoxide, electrical resistance decreases, and this 
triggers an alarm.
Electrochemical: Electrodes immersed in a chemical solution
sense changes in current when they come into contact with carbon
monoxide, and this change triggers the alarm.