The present invention relates to a sensor for and a method of detecting carbon monoxide in gas streams containing hydrogen. The sensor acts as a fuel cell and is comprised of a centrally placed membrane electrode assembly upon each side of which is positioned a current collector which has gas inlets that allow gas to flow to the membrane electrode assembly. Plates are positioned on each of the exterior surfaces of the current collectors such that when assembled, one side of the CO sensor forms an anode and the other side forms a cathode. At a constant voltage, a sample gas passes through the sensor such that low levels of Platinum on the sensor facilitate the detection of carbon monoxide. A reader attached to the sensor interprets the concentration of carbon monoxide and air is passed through the sensor for recalibration as needed.