Carbon monoxide detector

A carbon monoxide detector or CO detector is a device that detects the presence of the carbon monoxide (CO) gas in order to prevent carbon monoxide poisoning. In the late 1990s Underwriters Laboratories changed their definition of a single station CO detector with a sound device in it to a carbon monoxide (CO) alarm. This applies to all CO safety alarms that meet UL 2034 standard[1]; however for passive indicators and system devices that meet UL 2075, UL refers to these as carbon monoxide detectors.

CO is a colorless, tasteless and odorless compound produced by incomplete combustion of carbon-containing materials. It is often referred to as the "silent killer" because it is virtually undetectable by humans without using detection technology and, in a study by Underwriters Laboratories, "Sixty percent of Americans could not identify any potential signs of a CO leak in the home".[2] 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.[3]

CO detectors are 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, dual smoke/CO detectors are also sold.[4] Smoke detectors warn of smoldering or flaming fires by detecting the smoke they generate, whereas CO detectors detect and warn people about dangerous CO buildup caused, for example, by a malfunctioning fuel-burning device. 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.[5]

Carbon Monoxide detector connected to a North American power outlet
Carbon monoxide alarm
Carbon monoxide alarm


The devices, which retail for $15–$60 USD and are widely available, can either be battery-operated or AC powered (with or without a battery backup). Battery lifetimes have been increasing as the technology has developed and certain battery-powered devices now advertise a battery lifetime of up to 10 years. All CO detectors have "test" buttons like smoke detectors.

CO detectors can be placed near the ceiling or near the floor because CO is very close to the same density as air.[6][7]

Since CO is colorless, tasteless and odorless (unlike smoke from a fire), detection in a home environment is impossible without such a warning device. It is a highly toxic inhalant and attaches to the hemoglobin (in the blood stream) with an affinity 200x stronger than oxygen,[8] producing inadequate amounts of oxygen traveling through the body.

When carbon monoxide detectors were introduced into the market, they had a limited lifespan of 2 years. However technology developments have increased this and many now advertise up to 10 years.[9] Newer models are designed to signal a need to be replaced after that time-span although there are many instances of detectors operating far beyond this point.

According to the 2005 edition of the carbon monoxide guidelines, NFPA 720,[10] published by the National Fire Protection Association, sections and, all CO detectors “shall be centrally located outside of each separate sleeping area in the immediate vicinity of the bedrooms,” and each detector “shall be located on the wall, ceiling or other location as specified in the installation instructions that accompany the unit.”

According to the 2009 edition of the IRC,[11] published by the International Code Council, section R315.1, "For new construction, an approved carbon monoxide alarm shall be installed outside of each separate sleeping area in the immediate vicinity of the bedrooms in dwelling units within which fuel-fired appliances are installed and in dwelling units that have attached garages", and section 315.2, "Where work requiring a permit occurs in existing dwellings that have attached garages or in existing dwellings within which fuel-fired appliances exist, carbon monoxide alarms shall be provided in accordance with Section R315.1."

Installation locations vary by manufacturer. Manufacturers’ recommendations differ to a certain degree based on research conducted with each one’s specific detector. Therefore, make sure to read the provided installation manual for each detector before installing.

CO detectors are available as stand-alone models or system-connected, monitored devices.[12] System-connected detectors, which can be wired to either a security or fire panel, are monitored by a central station. In case the residence is empty, the residents are sleeping or occupants are already suffering from the effects of CO, the central station can be alerted to the high concentrations of CO gas and can send the proper authorities to investigate.

The gas sensors in CO alarms have a limited and indeterminable life span, typically two to five years. The test button on a CO alarm only tests the battery and circuitry, not the sensor. CO alarms should be tested with an external source of calibrated test gas, as recommended by the latest version of NFPA 720. Alarms over five years old should be replaced but they should be checked on installation and at least annually during the manufacturers warranty period.


Early designs were basically a white pad which would fade to a brownish or blackish color if carbon monoxide was present. Such chemical detectors were cheap and were widely available, but only give a visual warning of a problem. 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) the detector will not sound an alarm for many tens of minutes. At 400 parts per million (PPM), the alarm will sound 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 relatively common sources of carbon monoxide such as cigarette smoke.

There are four types of sensors available and they vary in cost, accuracy and speed of response,[13] listed below. The latter three types include sensor elements that typically last up to 10 years. At least one CO detector is available which includes a battery and sensor in a replaceable module. Most CO detectors do not have replaceable sensors.


The detector consists of a pad of a coloured chemical which changes colour upon reaction with carbon monoxide. They only provide a qualitative warning of the gas however. The main advantage of these detectors is that they are the lowest cost, but the downside is that they also offer the lowest level of protection.

One reaction used for carbon monoxide detection is potassium disulfitopalladate (II) catalytic oxidation:

As reaction progresses, atomic palladium release causes the color to change from yellow to brown to black.


A biomimetic sensor works in a fashion similar to hemoglobin which darkens in the presence of CO proportional to the amount of carbon monoxide in the surrounding environment. It uses cyclodextrins, a chromophore, and a number of metal salts. This can either be seen directly or connected to an infrared source of photons such as an IR LED and then monitored using a photodiode. Battery lifespan usually lasts 2–3 years with conventional alkaline, but a lithium battery will last the life of the product. The biotechnology based sensors have a useful operational life of 6 years. These products were the first to enter the mass market, but because they cost more than other sensors they are mostly used in higher-end areas and RVs. The technology has been improved and is the most reliable technology, according to a report from Lawrence Berkeley National Laboratory.[14] The technology is the only one tested false alarm free and is preferred by those with larger facilities like hospitals, hotels and apartments that use air fresheners, alcohols and other disinfectants where the cost of one false alarm is very high. This technology was invented in the United States and is manufactured in California.


This is a type of fuel cell that instead of being designed to produce power, is designed to produce a signal current that is precisely related to the amount of the target gas (in this case carbon monoxide) in the atmosphere. Measurement of the current gives a measure of the concentration of carbon monoxide in the atmosphere. Essentially the electrochemical cell consists of a container, two electrodes, connection wires and an electrolyte - typically sulfuric acid. Carbon monoxide is oxidized at one electrode to carbon dioxide while oxygen is consumed at the other electrode. For carbon monoxide detection, the electrochemical cell has advantages over other technologies in that it has a highly accurate and linear output to carbon monoxide concentration, requires minimal power as it is operated at room temperature, and has a long lifetime (typically commercial available cells now have lifetimes of five years or greater). Until recently, the cost of these cells and concerns about their long term reliability had limited uptake of this technology in the marketplace, although these concerns are now largely overcome. This technology is now the dominant technology in USA and Europe.


Thin wires of the semiconductor tin dioxide on an insulating ceramic base provide a sensor monitored by an integrated circuit. This sensing element needs to be heated to approximately 400 °C in order to operate. Oxygen increases resistance of the tin dioxide while carbon monoxide reduces resistance. The integrated circuit monitors the resistance of the sensing element. Lifespans are approximately five to 10 years.

The large power demand of this sensor means that it is usually powered from the mains. A battery-powered, pulsed sensor is available with a lifetime in months.

This technology has traditionally found high utility in Japan and the far east with some market penetration in USA. However the superior performance of electrochemical cell technology is beginning to displace this technology.


Although all home detectors use an audible alarm signal as the primary indicator, some versions also offer a digital readout of the CO concentration, in parts per million. Typically, they can display both the current reading and a peak reading from memory of the highest level measured over a period of time. These advanced models cost somewhat more but are otherwise similar to the basic models.

The digital models offer the advantage of being able to observe levels that are below the alarm threshold, learn about levels that may have occurred during an absence, and assess the degree of hazard if the alarm sounds. They may also aid emergency responders in evaluating the level of past or ongoing exposure or danger.


Portable CO detectors are also available; these are typically used for professional applications or in some cases by consumers such as property managers for maintenance and diagnosis issues (i.e. sourcing a CO leak). Most offer real time measurements of CO down to a few ppm (usually shown on a digital display), and are more expensive than home safety CO detectors (e.g. ~$250 vs $25). There are two types of portable detectors, one that is designed for aircraft, cars and trucks. They will warn the driver and passenger if there is a CO hazard. Another type is used by industrial hygienists and first responders. Digital, fast responding portable type CO detectors are usually a better choice for real time "on the go" applications as they respond to low levels of CO in seconds rather than minutes or hours (which is the case for UL2034 listed residential alarm).


Wireless home safety solutions are available that link carbon monoxide detectors to vibrating pillow pads, strobes or a remote warning handset. This allows those with impediments such as hard of hearing, partially sighted, heavy sleepers or the infirm the precious minutes to wake up and get out in the event of carbon monoxide in their property.

Legislation in the United States

In the U.S. (as of January 2017) 32 states have enacted statutes regarding carbon monoxide detectors, and another 11 have promulgated regulations on CO detectors[15], as well as in Washington, D.C. and New York City. In Canada CO alarm requirements came into force on October 15, 2014 in Ontario[16], there is a strong movement in Alberta to make CO detectors mandatory in all homes.[17]

More and more states are legislating for their installation as a mandatory feature.[18]

House builders in Colorado are required to install carbon monoxide detectors in new homes in a bill signed into law in March 2009 by the state legislature. House Bill 1091 requires installation of the detectors in new and resold homes near bedrooms as well as rented apartments and homes. It took effect on July 1, 2009. The legislation was introduced after the death of Denver investment banker Parker Lofgren and his family. Lofgren, along with his wife and children were found dead in their home near Aspen, Colorado on Nov. 27, 2008, victims of carbon-monoxide poisoning.

In New York State, "Amanda's Law" (A6093A/C.367) requires one- and two-family residences which have fuel burning appliances to have at least one carbon monoxide alarm installed on the lowest story having a sleeping area, effective since February 22, 2010. Although homes built before Jan. 1, 2008 are allowed to have battery-powered alarms, homes built after that date need to have hard-wired alarms. In addition, New York State contractors have to install a carbon monoxide detector when replacing a fuel burning water heater or furnace if the home is without an alarm. The law is named for Amanda Hansen, a teenager who died from carbon monoxide poisoning from a defective boiler while at a sleepover at a friend's house.[19]

Alaska House Bill 351 requires a carbon monoxide detector be installed in dwelling units that contain or are serviced by a carbon based fuel appliance or other device that produces by products of combustion.

In July 2011, California required installation of carbon monoxide detectors in existing single-family homes, with multifamily homes following in 2013.[20] CA Law 2015 require all new installation of smoke and CO alarms to be 10 year non serviceable type.[21] Existing alarms may not need to be replaced for home owners, see local codes. Required alarm location also vary per local enforcing agencies.

In Maine all rental units must have carbon monoxide detectors and non rental homes are recommended but not required to have carbon monoxide detectors [22]


North America

The Canadian Mortgage and Housing Association reports, "The standards organizations of Canada (CSA) and the United States (Underwriters Laboratories or UL) have coordinated the writing of CO standards and product testing. The standards as of 2010 prohibit showing CO levels of less than 30 ppm on digital displays. The most recent standards also require the alarm to sound at higher levels of CO than with previous editions of the standard. The reasoning behind these changes is to reduce calls to fire stations, utilities and emergency response teams when the levels of CO are not life threatening. This change will also reduce the number of calls to these agencies due to detector inaccuracy or the presence of other gases. Consequently, new alarms will not sound at CO concentrations up to 70 ppm. Note that these concentrations are significantly in excess of the Canadian health guidelines,"[23] (and also in excess of US Occupational Safety and Health Administration (OSHA) Permissible exposure limits, which is 50 ppm.)[24]


In the UK a domestic/Type-B alarm compliant with BS EN 50291:2001 should emit an audible alarm after about 3 minutes exposure to 300 ppm CO, or 10 to 40 minutes at 100 ppm, or 60 to 90 minutes at 50 ppm.[25]


  1. ^ "Standard for Single and Multiple Station Carbon Monoxide Alarms". UL. Retrieved 2017-10-22.
  2. ^ "Archived copy". Archived from the original on 2016-03-06. Retrieved 2016-02-28.CS1 maint: Archived copy as title (link)
  3. ^ NFPA 720: Standard for the Installation of Household Carbon Monoxide (CO) Warning Equipment, 2005 Edition, Annex B Dangers of Carbon Monoxide, B.1 Carbon Monoxide, Table B.1 Symptoms of Carbon Monoxide Exposure Based on Concentration
  4. ^ "Carbon Monoxide Detectors Buying Guide". 2017-09-22. Retrieved 2017-10-22.
  5. ^ U.S. Consumer Product Safety Commission, Carbon Monoxide Detectors Can Save Lives (CPSC Document #5010), archived from the original on 2009-04-09, retrieved 2007-07-29
  6. ^ Metropolitan Utilities District, Carbon monoxide detectors, archived from the original on 2007-08-14, retrieved 2007-07-29
  7. ^ CO Alert, Placement of Carbon Monoxide Detectors Important, archived from the original on 2013-06-06, retrieved 2009-01-11
  8. ^ Guyton A C: Medical Physiology 12ed. 2010, page 502
  9. ^ "Kidde Sealed Lithium Battery Power Carbon Monoxide Alarm with Digital Display C3010D". Retrieved May 10, 2016.
  10. ^ NFPA 720: Standard for the Installation of Household Carbon Monoxide (CO) Warning Equipment, 2005 Edition
  11. ^ 2009 International Residential Code® for One- and Two-family Dwellings
  12. ^ "Top 5 Things to Know About CO," LifeSafety magazine, Fall 2006
  13. ^ Guide to Prevent Carbon Monoxide Poisoning, retrieved 2007-07-29
  14. ^ Gundel, Lara A.; Michael G. Apte; Albert R. Nematollahi (1998). Carbon Monoxide Detector Technology Comparison: Response to Various Gases (PDF) (Technical report). Ernest Orlando Lawrence Berkeley National Laboratory. LBNL-40556. Retrieved 2014-01-14.
  15. ^ "Carbon Monoxide Detector Requirements, Laws and Regulations". National Conference of State Legislatures. 2017-04-03. Retrieved 2017-10-22.
  16. ^ "Carbon Monoxide Alarm Questions and Answers". Ministry of Community Safety and Correctional Services. Retrieved 2017-10-22.
  17. ^ Eva Ferguson (2017-01-06). "Carbon monoxide safety advocate to lobby Alberta to make detectors mandatory in Alberta". Calgary Sun. Retrieved 2017-10-22.
  18. ^
  19. ^ "Welcome Page". New York State Office of Fire Prevention & Control. Archived from the original on 2010-05-21. Retrieved 2010-03-18.
  20. ^ Senate Bill 183
  21. ^ "Archived copy" (PDF). Archived from the original (PDF) on 2016-05-06. Retrieved 2015-11-06.CS1 maint: Archived copy as title (link)
  22. ^
  23. ^ Canadian Mortgage and Housing Association Archived April 11, 2013, at the Wayback Machine
  24. ^ "Carbon monoxide". Centers for Disease Control and Prevention (CDC). April 11, 2016. Retrieved May 10, 2016.
  25. ^ Ei 204EN CO Alarm User Instructions

External links

Alarm sensor

In telecommunication, the term alarm sensor has the following meanings:

1. In communications systems, a device that can sense an abnormal condition within the system and provide a signal indicating the presence or nature of the abnormality to either a local or remote alarm indicator, and (b) may detect events ranging from a simple contact opening or closure to a time-phased automatic shutdown and restart cycle.

2. In a physical security system, an approved device used to indicate a change in the physical environment of a facility or a part thereof.

3. In electronic security systems, a physical device or change/presence of any electronic signal/logic which causes trigger to electronic circuit to perform application specific operation. In electronic alarm systems the use of this trigger event done by such devices is to turn on the alarm or siren producing sound and/or perform a security calling through telephone lines.

Note: Alarm sensors may also be redundant or chained, such as when one alarm sensor is used to protect the housing, cabling, or power protected by another alarm sensor.

Source: from Federal Standard 1037C and from MIL-STD-188 and from TRISHAM Software Systems

Catadioptric sensor

A catadioptric sensor is a visual sensor that contains mirrors (catoptrics) and lenses (dioptrics), a combined catadioptric system. These are panoramic sensors created by pointing a camera at a curved mirror.

Catalytic bead sensor

A catalytic bead sensor is a type of sensor that is used for combustible gas detection from the family of gas sensors known as pellistors.

Charlie Work

"Charlie Work" is the fourth episode of It's Always Sunny in Philadelphia’s tenth season. Featuring an uninterrupted seven minute long shot, the episode garnered critical acclaim from critics and fans and is considered one of the best episodes of Always Sunny. Contrary to popular belief, the episode is not a tribute to Birdman, but in fact, pays homage to HBO's True Detective.

Displacement receiver

A displacement receiver is a device that responds to or is sensitive to directed distance (displacement).

Examples of displacement receivers include carbon microphones, strain gauges, and pressure sensors or force sensors, which, to within an appropriate scale factor, respond to distance.

In music, certain music keyboards can be considered displacement receivers in the sense that they respond to displacement, rather than velocity (as is more commonly the case).

Examples of displacement-responding sensors include the mechanical action of tracker organs, as well as the force-sensing resistors found in music keyboards that had polyphonic aftertouch capability. Polyphonic aftertouch is no longer a feature of presently manufactured keyboards, but certain older models such as the Roland A50 featured a pressure sensing resistor, similar in principle-of-operation to a carbon microphone, in each key.

Electrochemical gas sensor

Electrochemical gas sensors are gas detectors that measure the concentration of a target gas by oxidizing or reducing the target gas at an electrode and measuring the resulting current.

Electromechanical film

Electromechanical Film is a thin membrane whose thickness is related to an electric voltage. It can be used as a pressure sensor, microphone, or a speaker. It can also convert electrical energy to vibration, functioning as an actuator.

Heat detector

A heat detector is a fire alarm device designed to respond when the convected thermal energy of a fire increases the temperature of a heat sensitive element. The thermal mass and conductivity of the element regulate the rate flow of heat into the element. All heat detectors have this thermal lag. Heat detectors have two main classifications of operation, "rate-of-rise" and "fixed temperature". The heat detector is used to help in the reduction of damaged property. It is triggered when temperature increases.


A humistor is a type of variable resistor whose resistance varies based on humidity.

Infrared point sensor

An infrared point sensor is a point gas detector based on the nondispersive infrared sensor technology.

Intelligent sensor

An intelligent sensor is a sensor that takes some predefined action when it senses the appropriate input (light, heat, sound, motion, touch, etc.).

List of sensors

This is a list of sensors sorted by sensor type.

Nest Labs

Nest Labs is an American manufacturer of smart home products including thermostats, smoke detectors, and security systems including smart doorbells and smart locks. Its flagship product, which was the company's first offering, is the Nest Learning Thermostat that was introduced in 2011. The product is programmable, self-learning, sensor-driven, and Wi-Fi-enabled – features that are often found in other Nest products. It was followed by the Nest Protect smoke and carbon monoxide detector in October 2013. After its acquisition of Dropcam in 2014, the company introduced its Nest Cam branding of security cameras beginning in June 2015.Co-founded by former Apple engineers Tony Fadell and Matt Rogers in 2010, the company quickly expanded to more than 130 employees by the end of 2012. Google acquired Nest Labs for US$3.2 billion in January 2014, when the company employed 280. As of late 2015, Nest employs more than 1,100 and has a primary engineering center in Seattle.


A pellistor is a solid-state device used to detect gases which are either combustible or which have a significant difference in thermal conductivity to that of air. The word "pellistor" is a combination of pellet and resistor.

Position sensor

A position sensor is any device that permits position measurement. It can either be an absolute position sensor or a relative one (displacement sensor). Position sensors can be linear, angular, or multi-axis.

Some position sensors available today:

Capacitive transducer

Capacitive displacement sensor

Eddy-current sensor

Ultrasonic sensor

Grating sensor

Hall effect sensor

Inductive non-contact position sensors

Laser Doppler vibrometer (optical)

Linear variable differential transformer (LVDT)

Multi-axis displacement transducer

Photodiode array

Piezo-electric transducer (piezo-electric)


Proximity sensor (optical)

Rotary encoder (angular)

Seismic displacement pick-up

String potentiometer (also known as string pot., string encoder, cable position transducer)

Confocal chromatic sensor

Potentiometric sensor

A potentiometric sensor is a type of chemical sensor that may be used to determine the analytical concentration of some components of the analyte gas or solution. These sensors measure the electrical potential of an electrode when no current is present.

Velocity receiver

A velocity receiver (velocity sensor) is a sensor that responds to velocity rather than absolute position. For example, dynamic microphones are velocity receivers. Likewise, many electronic keyboards used for music are velocity sensitive, and may be said to possess a velocity receiver in each key. Most of these function by measuring the time difference between switch closures at two different positions along the travel of each key.

There are two types of velocity receivers, moving coil and piezoelectric. The former contains a coil supported by springs and a permanently fixed magnet and require no output signal amplifiers. Movement causes the coil to move relative to the magnet, which in turn generates a voltage that is proportional to the velocity of that movement.

Piezoelectric sensor velocity receivers are similar to a piezoelectric accelerometer, except that the output of the device is proportional to the velocity of the transducer. Unlike the moving coil variety, piezoelectric sensors will likely require an amplifier due to the small generated signal.

Wavefront sensor

A wavefront sensor is a device for measuring the aberrations of an optical wavefront. Although an amplitude splitting interferometer such as the Michelson interferometer could be called a wavefront sensor, the term is normally applied to instruments that do not require an unaberrated reference beam to interfere with. They are commonly used in adaptive optics systems, lens testing and increasingly in ophthalmology.

There are several types of wavefront sensors, including:

Shack-Hartmann Wavefront sensor

Phase-Shifting Schlieren technique

Wavefront curvature sensor

Pyramid wavefront sensor

Common path interferometer

Foucault knife-edge test

Multilateral shearing interferometer

Ronchi tester

Shearing Interferometer

Yaw-rate sensor

A yaw-rate sensor is a gyroscopic device that measures a vehicle’s angular velocity around its vertical axis. The angle between the vehicle's heading and vehicle actual movement direction is called slip angle, which is related to the yaw rate.

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.