How do carbon monoxide sensors work

portable sensors are now available to monitor the air we breathe for such toxins as carbon monoxide, CO. As soon as the air contains more than a critical concentration of CO, the sensor alerts the householder, who then opens a window or identifies the source of the gas. 

At the heart of the sensor is a slab of doped transition-metal oxide. Its mode of operation is to detect the concentration of CO within the oxide slab, which is in direct proportion to the concentration of CO gas in the air surrounding it, according to Henry s law. 

in summary, CO gas partitions between the air and carefully formulated solid oxides. Henry s law dictates the amount of CO in the oxide. 

In general, Henry s law only applies over relatively small ranges of gas pressure. 

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