Understanding carbon dioxide detectors

Although much attention is often given to smoke detectors and fire alarms in the home and workplace, carbon dioxide detectors are also important in keeping indoor environments healthy. What is the role of these devices? Why is carbon dioxide detection important? Read on to learn more. 

A carbon dioxide detector

The importance of CO2 detection

What is carbon dioxide (CO2)?

Carbon dioxide is a colourless, odourless gas that is produced naturally through respiration and combustion processes. However, in indoor spaces, especially those that are poorly ventilated, CO2 levels can accumulate rapidly, reaching dangerous concentrations and degrading indoor air quality. Without an alarm, detector, or monitor in place to act as an early warning system, individuals may be unaware of this invisible threat.

Many people may confuse carbon dioxide (CO2) with carbon monoxide (CO). Despite their similarities with both being colourless, tasteless, odourless, and dangerous in large quantities, these gases are extremely different. Carbon dioxide is produced through natural processes and is essential for both plant and animal life on Earth. It is also created as a result of industrial processes and, when emitted in excess, is a greenhouse gas. Indoors, it is dangerous when it accumulates because it replaces oxygen.

Carbon monoxide, on the other hand, is produced through incomplete combustion. This means that when fuels like coal, natural gas, and wood are burned but do not fully burn, carbon monoxide is produced as a result. When inhaled through the lungs, carbon monoxide binds to haemoglobin, a protein that facilitates oxygen movement throughout the body. Widely known as the ‘silent killer’, prolonged exposure to carbon monoxide leads to symptoms like dizziness, headaches, fainting, and even death. It is always recommended to have a carbon monoxide detector or alarm in all indoor spaces10

Why CO2 levels matter

CO2 levels are an important indicator of air quality. High concentrations lead to health issues including headaches, dizziness, restlessness, and even asphyxiation if levels are high enough. Monitoring CO2 levels is an important step in ensuring a healthy indoor environment. As with all types of indoor air pollution, children, the elderly, pregnant women, and immunocompromised individuals are the most at risk.

Understandably so, scientific studies often focus on the dangers of fine particle pollution (from smoke and industry) and chemical pollution (like volatile organic compounds or VOCs). Previous studies indicated that CO2 levels would have to reach 5,000 parts per million (ppm), a very high concentration, before posing any danger to human or animal health. New studies, however, are finding that CO2 levels of just 1,000 ppm could be enough to lead to negative effects on health, even if the exposure is short-term1.

One such study exposed participants to three, 2.5-hour sessions of 600 ppm, 1,000 ppm, and 2,500 ppm of CO2 in an office-like chamber. The study observed ‘moderate and statistically significant decrements’ in decision-making performance at 1,000 ppm and ‘large and statistically significant reductions’ at 2,500 ppm2.

Another study found that exposure to elevated CO2 levels impacts sleep quality. The study reported ‘significantly reduced’ sleep quality when participants slept in environments containing 1,000 ppm and 1,300 ppm of CO2. Sleep quality and efficiency decreased by 1.3% and 1.8%, respectively. Sleep duration was also reduced. This indicates that elevated levels of CO2 promotes increased stress levels and sympathetic activity on the body3.

An additional study found that high CO2 levels decrease worker performance. It found that when CO2 levels were lower, employees’ test scores increased by 12%. In one of the buildings that were tested as part of the study, workers performed 60% under lower-CO2 conditions, completing tests in 8.2 minutes on average compared to 13.3 minutes under higher CO2 levels4.

High-risk environments for CO2

Certain environments pose higher risks than others of elevated CO2 levels. Industrial settings, agricultural facilities, and indoor spaces with poor ventilation (including homes and professional settings) pose some of the greatest risk for users of these spaces. In places like this, CO2 detectors are invaluable, allowing users of the space to control their exposure to unsafe levels of harmful gases and ensure safety in the home and workplace. It is also an indicator of whether or not there is sufficient ventilation.

Types of carbon dioxide detectors and how they work

Carbon dioxide detectors, also referred to as CO2 sensors, are typically categorised into three groups, each of which have their advantages and disadvantages5:

Non-dispersive infrared (NDIR) CO2 sensors

This type of sensor uses specific wavelengths of light to determine the concentrations of CO2 present in the air. Air enters the sensor, the sensor activates a light set at a specific wavelength at one end, and a receptacle at the other end measures the amount of light made it to the other side. The amount of light that is absorbed is determined by the quantity of CO2 present in the air: the more CO2 that is present, the more light gets absorbed. This is the same technology used in the Eoleaf Smart CO2 sensor.

  • Pros: long-lasting and durable, known for their accuracy and reliability, no interference from other substances, perfect for detecting common CO2 concentrations (around 1000 ppm)
  • Cons: sensitive to humidity and temperature
An NDIR CO2 detector

Source 6

Electrochemical CO2 sensors

Electrochemical CO2 sensors use electrical current or conductivity to measure CO2 concentrations in the air. When CO2 enters the sensor, a chemical reaction occurs, causing the sensor to undergo an electrical change. This may include picking up a new electrical current, changing an existing electrical current, or changing how the sensor carries an electrical current. The type and amount of electrical change is how the sensor determines the amount of CO2.

  • Pros: less vulnerable to humidity and temperature changes, provides visual indication of CO2 levels
  • Cons: interference from other substances may occur, battery and general lifespan do not last as long as other sensors
An electrochemical CO2 sensor

Source 7

Metal oxide semiconductor (MOS) sensors

The final type of CO2 sensor uses resistivity (or conductivity) of metal compounds present in a metal strip of film that is exposed to the air. The electric current running through the strip interacts when the CO2 comes into contact with it, the conductivity of the metal is altered, creating a change that determines the concentration of CO2.

  • Pros: simple design
  • Cons: sensitive to humidity and temperature, more often used for higher, less common CO2 concentrations (>2000 ppm)
An MOS CO2 sensor

Source 8

Calibration and maintenance

When purchasing a CO2 sensor, ensure that you follow the manufacturer’s instructions regarding calibration, safety, and maintenance. This will guarantee your CO2 detector’s accuracy and longevity. Perform regular battery checks and availability of spare parts. Be sure that it is possible to purchase a new battery if needed.

Installation tips for CO2 detectors and alarms

Ideal locations for installation

Just like placing an air purifier, a CO2 sensor or detector should be placed in the right location for it to be optimally effective in its CO2 detection. Place it in an area of your home or office that has the highest risk of CO2 accumulation. This means avoiding placing it too close to ventilation or exhaust systems or near windows or doors. Keep in mind that if your device requires regular calibration, it will need to be easily accessible9.

DIY vs. professional installation

CO2 detectors and alarms are generally easy to install and can be installed without professional experience. However, if you are concerned about proper placement to encourage improved indoor air quality, a professional may be able to help you in order to guarantee optimal performance and air quality.

Eoleaf air purifiers: an ideal solution for indoor indoor air quality

As mentioned above, high carbon dioxide levels in the home or workplace are an indicator of poor overall indoor air quality and pose a safety risk. CO2 is created by human respiration, the same method by which many airborne bacteria and viruses spread (as many of us remember from the COVID-19 pandemic). Viruses are spread through aerosol droplets released when humans breathe, talk, cough, sneeze, sing, or even eat. 

Eoleaf markets a high-end CO2 sensor which detects CO2 and alerts you whether or not you need to ventilate. More information can be found here: Eoleaf Smart CO2.

Eoleaf air purifiers have a sensor that detects all volatile organic compounds (VOCs), not just carbon dioxide. Furthermore, our air purifiers combat all types of air pollution: chemical pollution (like VOCs and ozone), germs (bacteria and viruses), fine particle pollution (PM10, PM2.5, PM0.1 from smoke, traffic, industry, or other sources), and allergens (dust and dust mites, pollen, pet hair and dander, mould and its spores). The best way to safeguard you, your loved ones, and your coworkers from the dangers of indoor air pollution is to remove all types with a high-quality air purifier from Eoleaf.

Eoleaf's product range

Frequently asked questions

What is a carbon dioxide detector, and how does it work?

A carbon dioxide detector is a device used to monitor the levels of carbon dioxide (CO2) in indoor spaces. There are three types of carbon dioxide detectors that work in different ways: NDIR CO2 sensors, electrochemical CO2 sensors, and MOS sensors. See the article above for more information on how each works.

Why is it important to monitor carbon dioxide levels in indoor environments?

Elevated carbon dioxide levels in the home or workplace are an indicator of poor overall indoor air quality and are a safety hazard. High concentrations of carbon dioxide replace oxygen indoors, leading to negative health effects. This may be due to many people congregating in one space and/or insufficient ventilation.

Can carbon dioxide detectors detect other gases?

No. Carbon dioxide detectors are used solely to monitor CO2 levels. Some devices, like Eoleaf air purifiers, will monitor levels of all harmful gases and volatile organic compounds (VOCs), including carbon dioxide.

Where should I install a carbon dioxide detector for optimal performance?

A carbon dioxide detector should be placed in areas where CO2 levels tend to accumulate. Some of the best places may be kitchens, living rooms, and/or bedrooms. CO2 sensors should be installed away from ventilation/exhaust systems, windows, and doors.

How often do carbon dioxide detectors need to be calibrated or replaced?

Always follow the manufacturer’s recommendations regarding calibration and/or replacements. Instructions vary depending upon the model and device.

How do carbon dioxide levels affect health, and what symptoms should I look out for?

High carbon dioxide levels affect health in a variety of ways including causing headaches, dizziness, restlessness, and even asphyxiation (if levels are extreme). Elevated CO2 levels and poor indoor air quality in general are also associated with lower productivity and levels of concentration and poor sleep quality.

What is the difference between a chemical CO2 detector and an infrared CO2 detector?

A chemical CO2 detector, also known as an electrochemical CO2 sensor, uses electrical current or conductivity to measure CO2 concentrations in the air. An infrared CO2 detector, also known as a non-dispersive infrared (NDIR) CO2 sensor or monitor, uses specific wavelengths of light to determine the concentrations of CO2 present in the air.

Can carbon dioxide detectors be integrated with smart home systems?

Absolutely! A carbon dioxide detector or monitor is an excellent addition to any home in order to improve indoor air quality.


1 Davis, N. (2019, July 8). Indoor carbon dioxide levels could be a health hazard, scientists warn. The Guardian. https://www.theguardian.com/environment/2019/jul/08/indoor-carbon-dioxide-levels-could-be-a-health-hazard-scientists-warn 

2 Satish U, Mendell MJ, Shekhar K, Hotchi T, Sullivan D, Streufert S, Fisk WJ. Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance. Environ Health Perspect. 2012 Dec;120(12):1671-7. doi: 10.1289/ehp.1104789. Epub 2012 Sep 20. PMID: 23008272; PMCID: PMC3548274.

3 Kang, M., Yan, Y., Guo, C., Liu, Y., Fan, X., Wargocki, P., & Lan, L. (2024). Ventilation causing an average CO2 concentration of 1,000 ppm negatively affects sleep: A field-lab study on healthy young people. Building and Environment, 249, 111118. doi:10.1016/j.buildenv.2023.111118

4 Study reveals C02 levels in offices are ‘silently damaging UK productivity.’ Work in Mind. (2018, May 12). https://workinmind.org/2018/12/05/study-reveals-c02-levels-in-offices-are-silently-damaging-uk-productivity/ 

5 Smith, D. (n.d.). CO2 sensors: Which type should you be looking for?. Kaiterra. https://learn.kaiterra.com/en/air-academy/carbon-dioxide-sensors 

6 Capteur de CO2 Portable Ndir 3 en 1 - détecteur de qualité de l’air. Signalétique Express. (n.d.). https://www.signaletique-express.fr/capteur-de-co2-portable-ndir-3-en-1-p-1238.html

7 MG811 carbon dioxide CO2 sensor module. Cytron Technologies Singapore. (n.d.). https://sg.cytron.io/p-mg811-carbon-dioxide-co2-sensor-module

8 Pickering, P., Tewari, S., & Twanow, C. (2018, April 10). Metal oxide gas sensing material and MEMS process. Fierce Electronics. https://www.fierceelectronics.com/components/metal-oxide-gas-sensing-material-and-mems-process 

9 Proper CO2 sensor location - where to mount your ndir sensor. Atlas Scientific. (2021, December 14). https://atlas-scientific.com/blog/co2-sensor-location/

10 Carbon monoxide vs carbon dioxide: What’s the difference? Aico. (2023, September 14). https://www.aico.co.uk/homeowner/articles/carbon-monoxide-vs-carbon-dioxide-whats-the-difference/

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