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A CO2 meter, also called a CO2 traffic light, CO2 detector or CO2 alarm, measures the concentration of carbon dioxide in the indoor air. The device determines the levels of CO2 in the room, given in ppm (parts per million). CO2 meters show you visually and/or acoustically when the CO2 concentration is very high that you must ventilate the room.

Most people spend a lot of time indoors. It is therefore not surprising that the indoor air quality has a major impact on our health and wellbeing. This is particularly helpful in the current corona pandemic: if you know the CO2 level, you can ventilate in good time and thus slow down the corona virus.

Stiftung Warentest tested 15 CO2 measuring instruments in its 02/2022 issue. One of the test winners among the measuring devices is the AirCO2ntrol 5000 from TFA Dostmann.

CO2 is not only a climate killer, but also an essential indicator of air quality in schools, public buildings, offices and homes. With a measuring device for CO2, you too can ensure optimal air quality in your rooms.

CO2 measuring devices for schools

In our guide to CO2 measuring devices, we have compiled a lot of information and explain how the CO2 concentration is related to indoor air quality and an increased risk of transmission of the coronavirus (COVID-19).

Buy CO2 meters from the manufacturer

Our CO2 meters monitor the CO2 concentration level in schools and classrooms, in offices and meeting rooms, homes and other indoor settings. CO2 traffic lights thus make a decisive contribution to indoor air quality. In our online retailer area you can find out where you can purchase CO2 meters from TFA Dostmann.

Guide to CO2 measuring devices

We are all very familiar with this: poor ventilated flats, stuffy classrooms or conference rooms with stale air. The reason for this “thick air” is primarily the exhaled carbon dioxide. Carbon dioxide is an odourless and tasteless gas.

Consistent ventilation in the corona pandemic

A research group at the Technical University of Berlin has discovered that high CO2 levels are an indicator for possible virus-laden aerosol concentrations in the room air. With a high CO2 value, one can conclude that there is a lot of exhaled air and/or that there has been no air exchange (ventilation) for a long time.

Thus, CO2 meters for schools, public buildings and offices are not only helpful devices for better indoor air quality and supports our ability to concentrate, but also increase hygiene standards and protect against viruses such as the coronavirus. Read more about the connection between coronavirus and indoor climate.

CO2 meters under test

In its 02/2022 issue, Stiftung Warentest tested 15 CO2 measuring devices for indoor use. The AIRCO2NRTOL 5000 from TFA Dostmann achieved with another model a first place among the CO2 measuring devices with a rating of “good (1.8)”.

The model from TFA measured very accurately in the test and secured the top rating of “very good (1.2)” in the “carbon dioxide measurement” category.

The device also scored with the individual setting of threshold values, the possibility of saving the measured values and a clear traffic light system.

Finally, the device includes an integrated thermometer and hygrometer for determining room temperature and humidity. Both values are important for a healthy and comfortable living environment and for the prevention of mold growth.

Where are CO2 meters most useful?

There are a variety of reasons for CO2 monitoring in business premises, public and residential buildings.

CO2 traffic lights for schools and classrooms

High levels of Carbon dioxide are only noticeable to people through the negative effect on the human body which includes:

  • Indisposition
  • Lack of concentration
  • Drop in performance

From 800 ppm, the air is considered polluted. Performance, concentration and well-being are already impaired at a concentration of 1,200 ppm carbon dioxide. In closed rooms where there are often many people, such as classrooms, teaching rooms, etc., values of 2,000 to 3,000 ppm carbon dioxide occur after a short time if the room is not ventilated properly.

In addition, the coronavirus can spread faster in closed rooms. Here, a high CO2 content is inferred to mean a high aerosol concentration and thus the greater probability of virus transmission.

CO2-Messgeräte für Räume wie Klassenzimmer.

CO2 measuring devices for classrooms

With our CO2 traffic lights, you can reliably measure the carbon dioxide concentration in classrooms and specialist practical areas such as science labs, art and music rooms. Only with the help of these measured values can proper ventilation take place or the use of air filter systems, for example, be correctly assessed and optimised.

This will improve the indoor air quality of school buildings and lead to healthier outcomes for students.

Our recommendation for schools:


  • Easy installation (mains plug or USB connection)
  • High-quality CO2 sensor (no maintenance or recalibration required)
  • Mobile and compact (can be easily taken from classroom to classroom)
  • Traffic light function (green/yellow/red) indicating the exact CO2 level
  • Adjustable alarm (depending on model, e.g. AirCO2ntrol Coach)

For more information about CO2 meters in schools and daycare centers, or if you would like to request a quote, please contact us.

CO2 measuring devices in companies and public buildings

In offices, training and conference rooms, workshops and recreation rooms, carbon dioxide is mainly produced by the breathing of the people in the room. The more people are present, the faster the levels of carbon dioxide increase. A CO2 measuring device with a traffic light signal prompts users to ventilate the room as needed at exactly the right time.

Ein CO2 Messgerät zeigt mit einer Ampel die Qualität der Raumluft an.

CO2 measuring devices for business premises and public buildings

CO2 monitoring is also necessary in many industrial areas. With the data on air quality provided by a measuring device, one can ensure appropriate measures for adequate ventilation.

CO2 measuring devices are particularly important in public spaces where it is necessary to protect the health and safety of people. These include hospitals, libraries, underground garages and tunnels.

CO2 data loggers are practical for long-term analysis. With these measuring devices with data logger function, you continuously monitor the carbon dioxide levels. The evaluation of the recording is done either directly on the device or via a software for processing and evaluating the measurement data on a computer.

What does a CO2 meter measure?

CO2 sensors cannot detect coronaviruses – but they indicate when it is time to ventilate a room. The measuring devices determine the carbon dioxide (CO2) content of the room air and indicate the indoor air quality.

CO2 Messgerät zur Anzeige der Luftqualität.

CO2 measuring device with clear display. It displays the CO2 value, the temperature, the relative humidity and the time.

CO2 meters usually have a display on which they show the measured values. In addition to the CO2 content of the room air, the room temperature and the relative humidity are usually also indicated. These meters have an integrated thermo-hygrometer.

All three values – CO2, temperature and humidity – are crucial for a good indoor climate.

Often the measured value is interpreted with a traffic light display and visualised in colour (red/yellow/green) or with smileys; either directly on the display or by additional coloured LEDs. Some measuring devices can save their measured values or transfer them to a computer. This makes series of measurements and analyses possible over the course of time.

How can CO2be measured?

A CO2 measuring device or CO2 data logger is needed for the ideal assessment and monitoring of the indoor climate. With the help of this measuring device, harmful carbon dioxide levels in the air can be detected quickly and easily. In this way, targeted countermeasures such as ventilation can be initiated to improve the indoor air.

Which sensor is used for CO2 measurement?

Good CO2 measuring devices usually work with an NDIR sensor. (nondispersive infrared sensor). Here, the precise content of carbon dioxide in the air is measured with the help of infrared radiation.

However, there are a few products on the market that work with a VOC sensor. A VOC sensor (volatile organic compounds) measures volatile organic compounds in the air in general. It reacts to a variety of different pollutants at the same time. It is useful as a pure indicator (whether the air is polluted by something), but it does not give an exact CO2 reading.

With regard to NDIR sensors, there are two types:

  • SingleBeam sensor (single channel sensor)
  • DualBeam sensor (two-channel sensor)

A single-beam sensor has the disadvantage that the CO2 measurement becomes inaccurate over time. Therefore, units with this sensor would have to be restarted or recalibrated under fresh air conditions every now and then. If this is not done, the measurement will shift further and further with permanent use.

On a DualBeam sensor a second control and calibration measurement always take place in addition to the regular measurement. The sensor adjusts itself independently and automatically.

Devices with DualBeam sensors therefore usually provide a more reliable measurement and also do not need to be restarted or recalibrated regularly. TFA’s CO2 meters mainly work with a DualBeam NDIR sensor.

What CO2 value is good?

The following CO2 concentrations apply to buildings with high occupation, e.g. schools, offices, hospitals, restaurants and all types of public buildings::

  • Optimal air quality: CO2 concentration is below 800 ppm.
  • Average air quality: CO2 concentration is between 800 ppm and 1,200/1,400 ppm.
  • Poor air quality: CO2 concentration is above 1,200/1,400 ppm.

The ideal air quality is in the measuring range of 400 – 450 ppm

How does the CO2 detector indicate the air quality?

When checking the content with a CO2 alarm, the measurement is permanent. Depending on the model, the CO2 meters indicate critical carbon dioxide concentrations visually and/or acoustically.

Can a CO2 meter warn of coronaviruses?

CO2 traffic lights cannot give warnings on viruses. A CO2 meter cannot measure coronaviruses or aerosols. The device is only intended to help achieve good indoor air quality. In addition, researchers have discovered that the higher the CO2 level, the higher the probability of contracting the coronavirus via infectious aerosols.

CO and CO2: What is the difference?

Many people confuse carbon monoxide (CO) with carbon dioxide (CO2). Both gases are transparent, odourless and tasteless and occur during incomplete combustion processes.

However, carbon monoxide (CO) is very dangerous even in much smaller concentrations. The CO level in the room increases rapidly if, for example, you heat with a wood stove and the exhaust air system is not working properly. Within a very short time, symptoms such as dizziness, nausea and even unconsciousness can occur. With heavy CO exposure, just a few breaths can lead to carbon monoxide poisoning and thus death by suffocation. CO (carbon monoxide) is not indicated by CO2 measuring devices.

Frequently asked questions about CO2 measuring devices

You will find answers to frequently asked questions about the CO2 sensors here:

When buying a measuring device, pay attention to measuring functions, measured variables, voltage supply, measuring range, application range, accuracy and the display. Read more in our CO2 meter guidebook.

Above 800 ppm, the air is considered polluted. Learn more about how the CO2 value determines the indoor air quality here.

Carbon dioxide can be lethal. CO2 concentrations of more than 20,000 ppm can cause coughing. Levels above 100,000 ppm cause unconsciousness and tremors. Concentrations of more than 250,000 ppm become a lethal hazard as the high concentrations either behave like poison in the body or displace oxygen from the bloodstream.