Carbon Monoxide (CO) is a dangerous gas produced by incomplete combustion of fossil fuels such as gasoline, oil and coal. It is odorless, tasteless and invisible to the naked eye. It can build up to dangerous concentrations in confined areas without adequate ventilation such as auto shops, mining operations and ice arenas. Carbon Monoxide poisoning results in many deaths each year.

A co monitor detects levels of the gas and alarms if it exceeds safe limits. The alarm is usually a high-pitched sound similar to the sound of a lawnmower. Some models feature a digital display that reads the CO level in parts-per-million. These are more accurate than audible alarms but cost more.

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Most detectors are designed to work like smoke detectors with a sensor that samples air for CO molecules. A microprocessor monitors the readings and triggers an alarm if the concentration rises above safe limits. Many models also have a test button that alerts the user when the unit is working. Most detectors are powered by either wires to the building’s electrical system or by batteries.

There are several types of sensors available for CO monitors, including biomimetic, metal oxide semiconductor and electrochemical. Biomimetic detectors use color-changing gels that change the sensor’s light response to carbon monoxide. When the sensor changes color, it activates the alarm. Metal oxide semiconductor sensors have circuits applied to a silica chip that, when exposed to CO, cause the chip’s electrical resistance to drop, which triggers the alarm. Electrochemical sensors use electrodes immersed in a chemical solution that react to CO and trigger an alarm. All types of carbon monoxide detectors are required to meet minimum standards set by Underwriters Laboratories (UL).