Abstract: A dual gas sensor is described, having first and second working electrodes separated by a gas impermeable portion. The electrodes are preferably located on a gas permeable polymer support, with the gas impermeable portion being formed by compression of the permeable support. The sensor may also include one or more filters for location adjacent the electrodes to filter certain gases from the air. The preferred sensor is able to detect carbon monoxide and hydrogen sulfide. The sensor housing is formed with four connection pins, allowing a standard sensor housing to be used for dual sensors as well as single sensors having a dummy pin.