An exhaust gas analyser or exhaust carbon monoxide (CO) analyser is an instrument for the measurement of carbon monoxide among other gases in the exhaust, caused by an incorrect combustion, the Lambda coefficient measurement is the most common.

An oxygen sensor (or lambda sensor, where lambda refers to air–fuel equivalence ratio, usually denoted by λ) or probe or sond, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analysed.