A carbon dioxide detector is a device that detects the presence of CO, which is a colorless and odorless gas that can be fatal in even small concentrations. This type of detector is usually installed in areas that are regularly exposed to CO, such as breweries, pubs and labs. These detectors are available in fixed or portable designs. In the latter case they can be used as a safety measure by people who travel between work sites and need to have the flexibility to monitor their own personal levels of CO.

Voluntary performance standards exist for carbon monoxide detection, most notably Underwriters Laboratories (UL) standard 2034 in the United States. These require detectors to meet certain sensitivity and alarm characteristics to earn the UL label.

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Most CO detectors operate by a process called photometric sensing, which uses an infrared light beam to measure the amount of CO present within the chamber. The amount of light emitted is proportional to the level of CO, which can trigger an alarm when a dangerous threshold is reached.

Other methods for measuring CO concentrations use a similar principle to photometric sensors, detecting the molecule by its ability to chemically interact with hemoglobin. This is accomplished by placing a gel in the detector that absorbs CO and changes color when the gas is present.

Like all test equipment, CO detectors must be assessed and maintained periodically. Unfortunately, data on how often owners conduct this assessment is limited. It is likely that many do not conduct these assessments as often as recommended by manufacturers, if at all.