A carbon monoxide detector or CO detector is a device that detects the presence of carbon monoxide (CO) gas and can prevent carbon monoxide poisoning. In the late 1990s, Underwriters Laboratories changed the definition of a single-station carbon monoxide detector with a sound device to a carbon monoxide (CO) alarm. Applicable to all CO safety alarms that meet UL 2034 standards; However, for passive indicators and system devices that comply with UL 2075, UL refers to them as carbon monoxide detectors.
CO is a colorless, tasteless and odorless gas produced by incomplete combustion of carbon-containing materials. It is often referred to as the “silent killer” because it is virtually undetectable by humans. In a study by Underwriters Laboratories, “Sixty percent of Americans could not identify any potential signs of a CO leak in the home”. Elevated levels of CO can be dangerous to humans depending on the amount present and length of exposure. Smaller concentrations can be harmful over longer periods of time while increasing concentrations require diminishing exposure times to be harmful.
Carbon monoxide detector is designed to measure CO levels over time and sound an alarm before dangerous levels of CO accumulate in an environment, giving people adequate warning to safely ventilate the area or evacuate. Some system-connected detectors also alert a monitoring service that can dispatch emergency services if necessary.
While CO detectors do not serve as smoke detectors and vice versa, combined smoke/CO detectors are also sold. In the home, some common sources of CO include open flames, space heaters, water heaters, blocked chimneys or running a car or grill inside a garage.
The devices can either be battery-operated or AC powered (with or without a battery backup). Battery-powered devices advertise a battery lifetime of up to 10 years. The gas sensors in CO alarms have a limited life span, typically two to five years. Newer models are designed to signal a need to be replaced after a set time span. CO detectors all have “test” buttons like smoke detectors, but the test buttons only test the battery, electronic circuit and buzzer, not the alarm’s ability to sense gas.
According to the carbon monoxide guidelines of the National Fire Protection Association, CO detectors should be installed in each sleeping area in a dwelling, and each detector should be located “on the wall, ceiling or other location as specified in the installation instructions that accompany the unit”.
CO detectors are available as stand-alone models, or system-connected devices which can be monitored remotely.
Early designs used a chemical detector consisting of a white pad that faded to a brownish or blackish color in the presence of carbon monoxide. Such detectors are cheap, but only give a visual warning. As carbon monoxide related deaths increased during the 1990s, audible alarms became standard.
The alarm points on carbon monoxide detectors are not a simple alarm level (as in smoke detectors) but are a concentration-time function. At lower concentrations, e.g. 100 parts per million (PPM), the detector does not sound an alarm for many tens of minutes. At 400 PPM, the alarm sounds within a few minutes. This concentration-time function is intended to mimic the uptake of carbon monoxide in the body while also preventing false alarms due to brief bursts of carbon monoxide from relatively common sources such as cigarette smoke.
Four types of sensors are available, varying in cost, accuracy and speed of response. Most detectors do not have replaceable sensors.