Last updated: August 11, 2021

Carbon monoxide is a poisonous gas that is produced by barbecues, fireplaces, radiant heaters or cigarettes. As it is colourless and odourless, you can hardly detect it. With CO detectors, however, you are immediately alerted as soon as a critical CO concentration value is exceeded in the room. Our large CO detector test 2022 should help you find the best CO detector for you. We have compared standard and wireless CO detectors as well as CO detectors for the hearing impaired, gas detectors and portable CO detectors and CO smoke and/or heat detector combinations with each other and listed the respective advantages and disadvantages. This should help you with your purchase decision.



  • Carbon monoxide is a poisonous, colourless and odourless gas that is produced when substances containing carbon are burned. Even low concentrations can lead to carbon monoxide poisoning without being noticed.
  • CO detectors alert you as soon as the CO concentration in the room exceeds a certain critical value that can be harmful to you.
  • CO alarms usually only detect carbon monoxide. There are special gas detectors for gases such as butane, propane or methane and separate warning detectors for the gas carbon dioxide.

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Guide: Questions to ask yourself before buying a CO detector

What is carbon monoxide anyway?

Carbon monoxide is a colourless, odourless and tasteless poisonous gas with a density similar to air. It therefore spreads rather slowly in the room. In technical jargon, the term carbon monoxide or carbon monooxide is more commonly used. This chemical compound of carbon and oxygen with the structural formula CO is a colourless, odourless and tasteless toxic gas and therefore particularly dangerous. When you are asleep, you do not notice the gas and can suffocate. Carbon monoxide has a similar density to air, so it spreads very slowly through the room. Since it is slightly lighter than air, it still rises slowly. It is also flammable and burns with oxygen with a blue flame. The particle concentration or the proportion of carbon monoxide is indicated with the English term ppm (parts per million). The millionth part, just as a percentage is the hundredth part of something. 50 ppm thus corresponds to a concentration of 0.005 % of the room air.

How is carbon monoxide produced and what are the sources?

In general, carbon monoxide is produced whenever something is burnt. Barbecues, fireplaces, radiant heaters but also cigarettes are possible sources of carbon monoxide. Carbon monoxide is produced by the incomplete combustion of carbon-containing substances such as natural gas, biogas, light petrol, heavy oil, coal or biomass with insufficient oxygen supply. The concentration in residential buildings is usually between 0.5 and 5 ppm. In rooms with gas burners, however, the CO concentration can be as high as 15 ppm. Even in rooms with chimneys, there should not normally be higher concentrations if there is sufficient chimney draught, as the gas evaporates with the warm air from the chimney. Improperly functioning heating and exhaust systems and defective or improperly maintained appliances can be sources of carbon monoxide. If the flue of a fireplace or stove is not able to transport the CO gas out, a backflow occurs and the room fills with carbon monoxide unnoticed. The flue does not even have to be defective for this, it is enough if, for example, a bird or wasp nest blocks the exhaust air duct. Carbon monoxide is also produced when barbecuing with charcoal and wood fires in general. Propane-fired radiant heaters and the like also emit carbon monoxide gas. In addition, gas cookers, the burning of wood pellets, car exhaust from attached garages and any kind of ventilation equipment and generators powered by combustion engines are sources of carbon monoxide. But cigarette and shisha smoke also contain carbon monoxide. Just ten smoked cigarettes increase the CO concentration in a 30 m³ room by 22 ppm. In an assessment, the Federal Ministry for Risk Assessment (BfR) explicitly points out a high CO concentration in shisha smoke.

Symptoms and consequences of carbon monoxide exposure/poisoning

If you inhale a high concentration of the gas, it will quickly become fatal. But even if you are exposed to a low concentration over a certain period of time, this can lead to severe physical damage and death. Since CO is similar in structure to the oxygen molecule O², the toxic gas binds to haemoglobin when it is absorbed through the respiratory tract and thus prevents the transport of oxygen through the blood. The affected person becomes unconscious and dies from lack of oxygen. Sick people, especially heart patients and unborn children, are more sensitive than healthy adults. The Berlin Socio-Economic Panel (BSEP) found that foetal development is strongly affected. Newborns in regions with high CO pollution are almost 300 grams lighter than others. According to the latest findings, carbon monoxide poisoning (technically carbon monoxide intoxication) also increases the risk of developing Parkinson's disease by a factor of 8 to 9. The first symptoms of CO poisoning are nausea, headache, shortness of breath, dizziness and drowsiness. For further information, Wikipedia offers a detailed article on carbon monoxide intoxication, which is based on the following table on CO concentration and symptoms:
CO concentration symptoms
35 ppm (0.0035%) headache and dizziness within 6-8 hours
100 ppm (0.01%) mild headache in 2-3 hours
200 ppm (0.02%) Mild headache within 2-3 hours, loss of judgement
400 ppm (0.04%) Severe headache within 1-2 hours
800 ppm (0.0%) Dizziness, nausea and cramps within 45 min, unconsciousness within 2 hours
1.600 ppm (0.16%) headache, increased heart rate, dizziness and nausea within 20 min, death in less than 2 hours
3,200 ppm (0.32%) headache, dizziness and nausea in 5-10 minutes, death within 30 minutes
6.400 ppm (0.64%) headache and dizziness in 1-2 min, seizures, respiratory arrest and death in less than 20 min
12,800 ppm (1.28%) unconsciousness after 2-3 breath

If you experience symptoms of carbon monoxide poisoning, call 911 and move away from possible CO sources immediately. If you suspect that someone is suffering from carbon monoxide intoxication, take care to protect yourself while rescuing them from the danger zone as quickly as possible. If the victim is unconscious but still breathing, place them in the recovery position. In case of cardiac arrest, resuscitation must be performed. The emergency doctor can then take further steps. The carbon monoxide content in the blood halves by itself within about four hours, but depending on the degree of poisoning, further treatment may be essential for survival. The affected person is usually intubated and ventilated with 100% oxygen. Hyperbaric oxygen treatment is also possible. In this case, the patient is ventilated with oxygen through tubes in a pressure chamber. In both cases, the carbon monoxide is displaced from the bloodstream.

Is a CO detector useful for you?

Basically, a CO detector is useful if there are possible sources of carbon monoxide leakage. Hospital data on cases of toxic effects of carbon monoxide on affected persons show that the documented number of cases in Germany more than doubled from 2000 to 2015. And this to almost 3500, with an upward trend. The number of unreported cases is probably much higher. It makes sense to have one or more CO alarms if there are potential sources of carbon monoxide emissions in the household. For example, do you heat with gas or have a fireplace in your living room? Do you cook with gas or do you have other appliances that run on gas or a combustion engine in general? Do you live in an older house where there is a possibility that the exhaust air system or the heating system are no longer in optimal condition? Then we recommend that you install a carbon monoxide alarm to be on the safe side. Even if you like to smoke cigarettes or shisha in your home, a CO alarm makes sense. As you have learned above, the CO concentration in the room can increase considerably due to the smoke.

What does a good carbon monoxide detector have to offer?

Most important are the service life, some features such as display, memory or test function as well as quality seals. The service life of the CO sensor is an important criterion. High-quality carbon monoxide detectors have a lifespan of 7 to 10 years. Inferior sensors, on the other hand, only last about one year. This means you incur many times the additional costs and, from an economic and safety point of view, such cheap products do not make sense either. Some manufacturers offer an additional guarantee of usually 5 years. You should make sure that the alarm is equipped with a permanently installed lithium battery. Then you don't have to worry about replacing the batteries, because the life span is the same as that of the CO sensor. If you nevertheless choose a detector with a replaceable 9-volt battery, for example, it should definitely have a "low bat" indicator. Detectors with displays are preferable. You can then easily read off the CO concentration or other information. For this purpose, the display must be large enough, easy to read and, above all, clearly visible. A display with backlighting is ideal. A useful feature is the peak value and/or event memory function. On the display you can see, even after a longer absence, whether there was an increase in the CO concentration, what the peak value of the concentration was and whether an alarm was triggered. In addition, your CO alarm should offer a possibility to test it. Some detectors test themselves automatically, others have a test button. In general, you should not just blindly rely on technology, but be able to test the CO sensor in some way. After all, it's about your health and safety. Good carbon monoxide detectors do not simply sound the alarm at a certain CO level. Most have several alarm levels. But when and after what time the alarm goes off can vary. For a healthy adult, the levels 50, 100 and 300 ppm are sufficient. In a child's room, it is advisable to consider installing lower alarm levels with a shorter time delay, e.g. 30, 43, 80 and >150 ppm. Also look for quality seals! High-quality alarms are manufactured, tested and approved according to national or international guidelines. If your CO detector has a TÜV, VdS and/or CE seal, this is always a sign of quality. In addition, your alarm should be certified according to EU directives. Besides easy handling and installation of the CO detector, the volume of the CO alarm is of essential importance. The warning detector is of little use to you if the alarm is so quiet that you can't hear it. Most detectors are around 85 dB. However, the alarm should not be any quieter. Detailed instructions in German and/or at least English are another important criterion. The alarm will not help you if you cannot operate it (correctly) because the instructions are in Chinese or Russian. Unless you can read Mandarin or Cyrillic. If you want to install several CO detectors, make sure that they can be networked via radio and are compatible. Especially if you live in a large building and the rooms are far apart. You should also consider the size of the room in which you want to install a CO detector. Not all alarms are designed for all room sizes. Check the requirements for the CO detector with regard to the room size, otherwise it may be ineffective!

How many CO detectors should you buy?

Every room where there is a potential source of CO leakage should be secured. For example, if you have a gas heater in the basement, a gas cooker in the kitchen and a gas heater in the conservatory, you should definitely equip these rooms with CO alarms. Radio-networked warning detectors are recommended, as all detectors sound an alarm as soon as a detector measures a dangerous CO concentration. Basically, you should consider which sources of CO gas there are in your home and protect these rooms with carbon monoxide alarms. It may also make sense to secure a room with an alarm where there is not a direct source of carbon monoxide. Since this poisonous gas rises very slowly, it can happen that it "sloshes" into a room unnoticed. So think beforehand about the rooms in which you need a carbon monoxide alarm.

What standards should your CO detector meet and what certifications are there?

The EU standard EN 50291 should be met in any case. A CE mark, a TÜV and VdS seal are further quality features. The European standard EN 50291 generally regulates the requirements of electrical CO measuring devices for operation in residential buildings in the areas of construction, test procedures and operating behaviour. If you want to find out more about this standard, you can do so on the website of the German Association for Electrical, Electronic & Information Technologies (VDE). However, the text of the standard costs.. The CE mark indicates that the product complies with the European directives that apply to the specific product. Although this seal is not a test seal but an administrative mark, it still indicates that European directives are complied with. You are probably familiar with the TÜV seal. The TÜV tests technical products neutrally, expertly and independently and certifies products that meet the high requirements. The "TÜV-tested" seal is at least colloquially a seal of quality, but it is relatively rare for CO detectors. A certification of the VdS (Vertrauen durch Sicherheit) damage prevention products of the civil security market as well as guard and security companies. A VdS seal indicates that the product-specific requirements of the CO detector exceed those of the European standard.

Decision: What types of CO detectors are there and which is the right one for you?

Basically, you can distinguish between the following types of carbon monoxide detectors:

  • Standard CO detector
  • Radio CO detectors
  • CO detectors for the hearing impaired
  • CO smoke and/or heat detector combinations
  • Gas detectors
  • Portable/mobile CO detectors

The detector types have different functions or areas of application and thus individual advantages and disadvantages. In addition, there are combinations of the different detector types. Depending on how big your home is, in which room you want to install a carbon monoxide detector or against which dangers you want to protect yourself additionally, different functions make sense. You may also need a CO alarm for your caravan or want to use it flexibly in different places. The following section will help you to find out which type of carbon monoxide detector is suitable for your needs. For this purpose, we will present the types of CO detectors listed above and clearly outline what their advantages and disadvantages are in each case.

What are the advantages and disadvantages of standard CO detectors?

Standard CO detectors or stand-alone detectors can do exactly one thing: sound the alarm as soon as the concentration of carbon monoxide in the room exceeds a certain level. But there are also models that are additionally equipped with some very useful functions. Since even a low, not immediately lethal concentration of CO gas can lead to physical damage over a certain period of time, the acoustic alarm of most warning detectors, for example, only goes off after 60 - 90 minutes in the case of a low CO concentration, and after 3 minutes in the case of a high concentration. There are also CO detectors with LCD displays or LED control lights for better monitoring of the carbon monoxide concentration, for example. The acoustic warning signal and features are of course also found in the other CO detector types and are only mentioned here as an advantage over not using CO detectors.

  • Acoustic warning signal when the CO level is too high
  • Various useful features
  • Comparatively inexpensive
  • May not be audible in large houses and halls
  • Only sounds when carbon monoxide is present
  • Usually fixed to the wall/ceiling

Features such as those mentioned above, (automatic) function testing or memory functions naturally have an impact on the price. As always, the manufacturer and the quality of the device also play a role. If you live in a large house or need CO detectors for (storage, production, etc.) halls, the alarm may be overheard despite its volume due to the distance or closed doors. In this case, you should use radio-networked CO detectors. We see the fact that a CO detector "only" reports CO as a disadvantage here only for the reason that combination devices with other (e.g. optical) sensors can also detect smoke and sound the alarm. A high CO concentration does not necessarily mean a fire. That's why you should use a smoke detector as a fire alarm; it's usually cheaper, too.

What can wireless CO detectors do and what are their advantages and disadvantages?

CO radio detectors can be linked to each other via an integrated or additionally available radio module. Via this module, the CO detectors can also communicate with other additional devices and thus form a complete home system. The problem of standard CO detectors in large houses or halls can be solved by radio networking. The warning detectors are coupled with each other via the radio module. If the CO concentration now rises in a room with a CO detector, it sends a signal to all devices connected to it, which then also trigger an alarm. In this way, an increase in carbon monoxide gas does not go unnoticed even if the alarm is triggered in a distant cellar or similar.

  • No alarm goes unnoticed (even in extensive/large buildings)
  • Several CO detectors, additional devices and other detectors can be radio-networked
  • Usually no separate power supply for the radio module necessary
  • Usually easy retrofitting of the radio module possible
  • Triggers "only" for carbon monoxide
  • Usually fixed to the wall/ceiling
  • Relatively high price for CO detector incl. radio module or retrofit module

It is therefore not only possible to link several CO detectors with each other, but also to integrate smoke detectors or detectors for other harmful gases into the system. This makes the radio-networked CO detector interesting for industry as well. Many companies have installed such systems in their warehouses and production halls. For private use, additional devices such as a vibration or optical signal for the hearing impaired can be embedded in the system. Many manufacturers state that the separate radio module can be easily retrofitted in just a few steps. In addition, the module is powered by the power supply of the carbon monoxide detector. This means no additional battery waste.

What are the advantages and disadvantages of CO detectors for the hearing impaired?

This type of detector is not actually a CO or smoke detector as such, but an additional device that can be embedded in the warning detector system via radio. However, since 15 - 16 million people in Germany are affected by hearing loss, depending on the source, we think it makes sense to present this solution to you. The prerequisite for the hearing-impaired alarm is radio-networked warning detectors. It does not matter whether CO, gas or smoke detectors or combinations of warning detectors are connected to each other in the network. At least the leading manufacturers guarantee a smooth signal exchange between the different radio detectors and with the additional device for the hearing impaired. Nevertheless, for safety's sake, you should make sure that the detector components come from the same manufacturer. As soon as a CO detector detects an increasing CO concentration, the warning detector for the hearing impaired alerts you visually via an intensive stroboscopic light. In addition, a vibration pad is connected, which is placed in the pillow. This ensures that you are woken up in case of danger.

  • Safe alarm system for the hearing-impaired
  • Usually emergency battery available (power failure)
  • Compatible with different and several detector types and can be wirelessly networked
  • Free-standing (within the scope of the cable length)
  • Wireless networking sometimes not very easy
  • Relatively high price (in addition to the actual warning detectors)

The warning detector is connected to the socket and can be placed flexibly in the room due to its relatively long connection cables (connection between device socket and device vibration pad) of 3 - 5 metres. In addition to the power connection, most manufacturers have equipped the device with a rechargeable battery or a 9-volt battery. This emergency power supply ensures that the alarm goes off reliably even in the event of a power failure. Even though the alarm for the hearing impaired is compatible with various smoke, gas and CO sensors, problems can occur during the first radio connection. For example, the website reports initial difficulties in establishing the first wireless connection with other components.

What can CO smoke and/or heat detector combinations do and what advantages and disadvantages do they offer?

If, in addition to carbon monoxide, a warning is to be given about smoke development and fires, a combination detector with different sensors supposedly saves the installation of several detectors. Such multi-sensor detectors reduce the risk of false alarms by measuring carbon monoxide concentration in the room, smoke density and/or temperature rise. However, only in the event of a fire alarm. If you have considered protecting yourself from fires as well as carbon monoxide poisoning, and don't want to plaster every room with warning detectors, a combination device might make sense. However, there are a few things to consider here. Basically, a combi device also measures the carbon monoxide concentration and sounds an alarm if a limit value is exceeded. But now you have to decide whether you want to use the alarm as a CO alarm or as a smoke alarm. This is because smoke moves quickly towards the ceiling with the warm air of a fire and carbon monoxide spreads very slowly because it has almost the same density as the air in the room. By the time the carbon monoxide reaches the ceiling, the whole room is usually already flooded. You also face this problem with a CO thermo-detector combination. Many products of this CO detector type are offered as "smoke and CO detectors" or "combined CO detectors". Usually, however, a closer look at the description reveals the actual area of application for the carbon monoxide sensor: Slowly spreading fires or sulphur fires have a relatively low smoke development, but produce carbon monoxide gas. Thus, the warning detector can also sound the alarm in these cases. Multi-sensor detectors are therefore often already offered as fire detectors, such as the 3-sensor combination from Bosch.

  • The risk of false alarms is reduced
  • Detects any type of fire
  • Inexpensive, medium-quality products available
  • Decision problem in the area of application
  • Very high price for high-quality products
  • As a pure CO detector, only useful for very low ceilings

As mentioned above, a combination device CAN be used as a pure CO warning device if it is mounted accordingly. The website www.testberichte.dekommt also concludes that such a combination device makes little sense as a CO detector, if only from a practical point of view. It can only reliably warn of one or the other. On the other hand, such a device makes sense in small rooms with very low ceilings, e.g. in a caravan or inside a boat. Here, the CO concentration can be measured better. However, we would like to point out that if you want to use a combi device as a pure CO detector, you must study the product thoroughly before purchasing it. If in doubt, we advise you to use two separate detectors.

What can gas detectors do and what are their advantages and disadvantages?

Gas detectors measure the concentration of various toxic gases and sound an alarm as soon as a limit value is exceeded. Gas detectors are available that detect methane and ethane (natural gas), propane and butane (liquid gas) or carbon monoxide and warn of excessive concentrations. Combination devices are also on offer. This leads to a well-known problem. As you can probably guess, carbon monoxide, natural gas and LPG have different densities. That is why it is necessary to mount the gas detector either on the wall, the ceiling or near the floor. A combination gas detector that detects carbon monoxide and liquid gas or carbon monoxide and natural gas with the respective sensors is therefore not very useful.

  • Detects different gases
  • Usually very easy to install
  • Decision problem in the area of application
  • Compared to the pure CO detector, relatively high power consumption
  • As a pure CO detector, only useful for very low ceilings

Gas detectors usually have to be connected to a socket. On the one hand, this simplifies installation; on the other hand, a gas detector requires more energy than a conventional CO or smoke detector. This is due to the fact that a wire inside the detector is made to glow by a continuous current supply. When a gas comes into contact with the glowing wire, heat is generated by combustion. If there is enough heat, the gas detector will sound the alarm. As with the CO smoke and/or heat detector combinations, we encounter the problem with the combi gas detector that different installation locations make sense for different gases. So it does not reliably warn you of different gases at the same time. It makes sense to install a gas alarm in small rooms with very low ceilings, e.g. in a mobile home or inside a boat. However, we would like to point out once again that if you want to use a combination device purely as a CO detector, you must study the product thoroughly before purchasing it. If in doubt, we advise you to use separate detectors.

What are the advantages and disadvantages of a portable/mobile CO alarm?

Portable CO detectors are often carried by fire brigades and rescue services during operations. But portable and free-standing CO detectors can also be useful for private use. For fire and rescue service personnel, small, portable carbon monoxide detectors are used to assess operational safety. These handheld devices are often very functionally designed and are therefore less suitable for use in the home. However, there are freestanding and portable CO detectors in modern or plain design that are indistinguishable from other warning detectors.

  • Functional, modern or plain design available
  • Flexible to use in different places
  • Combination of different sensors makes sense
  • Mostly no radio networking possible

A CO alarm that can be used flexibly in different rooms or taken along on holiday, in the car or caravan sounds sensible. In our opinion, it is. It would also make sense to combine a CO sensor with sensors for other toxic gases, smoke or heat. Depending on the area of application, you can place the alarm in the best place for it. But you have to know the behaviour of the respective gas. And again, you should not use a combination device in parallel for different gases and/or fires. The only shortcoming of portable or free-standing carbon monoxide alarms is that they usually lack the ability to be networked with other alarms and devices via radio.

Buying criteria: Use these factors to compare and evaluate CO detectors

The following article presents the factors you can use to compare and evaluate carbon monoxide detectors. This should help you decide whether a particular device is suitable for you or not. In summary, these are:

  • Product weight
  • Product dimensions
  • Room coverage
  • Operating temperature
  • Power supply
  • Sensor lifetime
  • LCD display
  • Battery level indicator
  • Control LED
  • Audible and visual alarm
  • Alarm levels
  • Alarm volume
  • Test function
  • Memory function
  • Certification
  • Warranty
  • Areas of application
  • Wall mounting / Stand mounting
  • Instructions D/E

In the following paragraphs you can read about the individual criteria and how you can classify them.

Product weight

This criterion is especially relevant for mobile CO detectors. The lighter a detector is, the more handy and practical it is for flexible use. For CO alarms that you mount on the wall, this criterion does not really matter. Your wall should be able to withstand any type of CO detector. However, if you are inclined towards a mobile CO alarm because you want to take it with you on holiday, for example, it is of course more practical if it is as light as possible. Weight is even more important for CO detectors that you want to carry with you all the time. This is the case, for example, with fire brigades and rescue services.

Product dimensions

The "size" of the warning device is not only important for mobile devices. The larger a wall-mounted CO detector is, the more it attracts attention. The larger the CO alarm is, the less practical it is. This applies mainly to mobile CO detectors. But free-standing detectors also take up unnecessary space. So why buy a large detector when you can have the same functions in a more compact form? A CO alarm that you mount on the wall should be easily visible and the display should be large enough and easy to read. However, its size should not attract attention and it should be discreet. With today's technological advances, you can use the following guiding principle as a guide: As small as possible but as big as necessary.

Room coverage

The room size should not exceed the detection range of the carbon monoxide sensor. Unfortunately, manufacturers do not always provide this information. Especially for large rooms, it is important to know the maximum detection range of a CO sensor. If the room size exceeds the specified maximum value, the alarm may not be triggered. Unfortunately, only a few manufacturers provide this information. The detection areas we have researched vary from 20 - 60 m². If you are not sure and want to equip a larger room with a CO detector, an e-mail to the manufacturer can help, or you can go to a specialist shop and ask a competent employee in person.

Operating temperature

Do you want to install a CO alarm in the cellar? Even though almost all alarms are operational from 0 °C, it may make sense to consider a warning device with a wider operating temperature range. Cellars without heating can get quite cold in winter. Likewise, smaller rooms can heat up considerably if they are exposed to strong sunlight during the day in summer. This can lead to the CO sensor not working properly and the alarm not being triggered. Or it can lead to false alarms. The smallest range in which CO sensors work properly, according to the manufacturer, is between 0 and 40 °C. Certain alarms have a wider range from -10 to a maximum of 50 °C. If you are unsure, first determine the room temperature with the help of a thermometer.

Power supply

It is not only for the sake of the environment that permanently installed lithium batteries make sense. Even if you are reminded to change the batteries via an LED or a display, this can be overlooked. Many CO detectors are powered by one to three AA batteries or a 9 volt block battery. When the batteries run out, most models will remind you. New batteries must then be inserted and the old ones disposed of. The danger here is that, despite the LED and/or display, this can simply be overlooked. After some time, you often no longer pay active attention to minor changes.. The newer models from the leading manufacturers are usually equipped with a permanently installed lithium battery. The service life is the same as that of the CO sensor. Therefore, you don't have to worry about the batteries. Moreover, one lithium battery and several AA or monobloc batteries only make a slight difference in terms of cost. Another option is to power the detector by plugging it into a wall socket. This is the case with many gas detectors, as they require a comparatively large amount of power.

Sensor service life

The service life (up to 10 years) of the CO sensor is one of the most important criteria. From an economic point of view alone, cheap products with a short service life (e.g. 1 year) do not make sense. It is more worthwhile to invest once in a quality product with a long service life. Many no-name products may seem like a bargain at first, but often have a very low life expectancy. In most cases, this is between one and three years. Then the CO sensor breaks down, the alarm no longer detects the gas and has to be replaced. Current products from leading manufacturers already achieve a sensor life expectancy of up to 10 years. These are a little more expensive to buy, but then you have a quality product and thus a device with a higher yield in this area.

Kohlenmonoxid Gas-Melder

When making such purchases, the quality should be in the foreground, not the price! It could save lives.

LCD display

Depending on the supplier and model, you can easily use various functions of the CO alarm via a display. Display the ppm value or the temperature, check the battery level, read out the memory, etc. Nowadays, pretty much every product has a display, even toothbrushes. With your CO detector, however, such a display is actually useful. Additional features that many detectors have can usually be controlled very easily via a display. Important features are presented below as additional criteria. Reading the ppm value or the peak value memory is not possible without a display. Your CO alarm should have a display in any case. A useful gimmick is a time-limited backlight to guarantee the readability of the display.

Battery level indicator

A battery level indicator is important! In any case, your CO detector should alert you in some way that the battery is running low. Many detectors use a red or yellow LED to draw your attention to a low battery level. This flashes or lights up permanently for a certain period of time. This is especially important for battery-operated devices where you have to change batteries frequently. If the CO alarm has a display, the battery level is shown continuously on some models. This way you can also see in advance how long the AA or lithium battery will last. An additional flashing LED when the battery level is low is also useful here. This reminds you even if you are not always actively checking the display.

Control LED

An LED should inform you of the operating status. Either permanently or at the latest in the event of a malfunction. Not all CO warning devices show you via a green flashing or permanently lit LED that everything is OK with your carbon monoxide detector. On the one hand, this would be a useful feature, but on the other hand, such a flashing light can be extremely annoying, especially in the bedroom. There is another solution for bedrooms. You can perform a manual test on many CO alarms, whereupon you will be informed via an LED whether your device is working properly. Other alarms are equipped with a self-test function. If this test reveals that any function is not working properly, this is automatically signalled by a red flashing or permanently lit LED. Some detectors also sound an alarm.

Acoustic and visual alarms

Visual signals are particularly important for the hearing impaired. However, you have to decide whether a flashing LED is sufficient or whether you need an additional module for the hearing impaired. This is also about the alarm in case of malfunctions. In addition to the acoustic alarm, some warning detectors also signal visually whether there is a CO danger or that something is wrong with your device. If a CO alarm is triggered, a visual alarm is useful for the hearing impaired. Whether a flashing LED is sufficient is another question. For the bedroom, we advise you to use an additional module for the hearing impaired. That will wake you up in any case. However, it is also possible that only short, regular alarm tones are emitted in the event of a malfunction. If this is less easy to detect for a hearing-impaired person, a visual signal can alert this person to the malfunction and appropriate steps can be taken. Since the danger here is not acute, an additional visual alarm can be an alternative to the expensive add-on module.

Alarm levels

For carbon monoxide alarms, there are legal requirements as to the concentrations above which the alarm must be triggered within a certain time. However, for small children, for example, it can be useful if the alarm is triggered earlier. The legal requirements according to the EU certification EN 50291 state that the CO alarm must alert you at carbon monoxide concentrations of 50, 100 and 300 ppm within a certain period of time. The exact data can be found in the table in the section Trivia - How does a CO detector work? However, small children, pregnant women and people with heart conditions are more sensitive to carbon monoxide and even a low concentration can cause damage. For rooms of affected persons, it is then advisable to pay attention to the alarm levels when buying a CO alarm. There are devices on the market that activate even at concentrations lower than the legal minimum requirements.

Alarm volume

The legal minimum volume of a CO alarm is 85 dB. So make sure that your CO detector does not fall below this value! Otherwise it will probably not be approved in Europe. The volume of CO detectors is usually given in dB at a distance. For example, a value of 85 dB at one metre means that the alarm has a volume of 85 dB when you stand one metre away from it. This is about the average volume of a petrol lawnmower. A value below this volume is not permitted by law. Therefore, you should also pay attention to this product information. Some louder CO alarms still reach 85 dB at a distance of three metres. However, much louder alarms are rather the exception.

Rauch-und CO-Melder

The volume of a CO detector is usually in the same range as that of a fire detector. The CO detector also hardly differs from the smoke detector in other properties, which is understandable since there is not much difference in the way they work. (Photo: leekris / 123RF)

Test function

You should be able to test your CO detector. How else do you know if it works? Most CO detectors are equipped with such a function. Whether you have to test manually using a test button or your detector has a self-test function. This way you can be sure that all functions are working properly. If something is not working properly, you will be notified by a visual and/or acoustic alarm. If your CO alarm is not equipped with either of these features, your only option is to buy a test gas. You should test your warning device in any case. Otherwise it may be useless.

Memory function

This function allows you to see whether an increased CO concentration was recorded or an alarm was triggered in your absence. If you are away for a while, for example on holiday, you can use the memory function to find out various things. Most warning devices show you whether an alarm was triggered in your absence. In addition, some CO detectors also record smaller increases in CO concentration and then display them on the peak value display. Even a small increase in CO concentration can be an indication of a leak or a CO source. With a peak value memory function, you will be notified of this possibility after your return and can get to the bottom of it. The storage period varies greatly across the models.


Certificates tell you whether a CO detector is approved in Europe and complies with national regulations. Your CO alarm should at least comply with the European standard 50291 from 2010. EN 50291-1:2010 are the minimum European requirements for a carbon monoxide alarm for domestic use. Your alarm should definitely comply with this standard. Note, however, that this standard only applies to private households. If you want to install your CO alarm in a caravan, motor home or boat, the warning device must also comply with the EN 50291-2:2010 standard. If both sub-standards are met, the manufacturer usually simply states "EN 50291 certified". You can read about the relevant standards and certifications in the section Guide - What standards should your CO detector meet and what certifications are there? If you decide on a CO smoke and/or heat detector combination or a gas detector, note that your detector must comply with other standards. If you want to be warned of other gases, temperature and smoke in addition to carbon monoxide, there are special standards for these.


A manufacturer's warranty, whether for 3 years or the entire service life, is a plus. The leading manufacturers actually always give a guarantee. Often over 3 - 5 years, with the newer models sometimes over the entire life of the CO sensor. This means you get a free repair or a replacement device if your alarm does break down.

Areas of use

Where you can use the CO alarm depends on the EU certification. In addition to warning devices exclusively for household use, some CO detectors can also be used in caravans, mobile homes and boats. This criterion is intended to show you where you can use your carbon monoxide detector if you are not familiar with the relevant EU standards and certifications. Although the areas of application are dependent on these standards, it is quite cumbersome to find out about every standard.

Not all carbon monoxide detectors can be used in all areas!

Facts worth knowing about CO detectors

How does a CO detector work?

The carbon monoxide detector has an electrochemical sensor that measures the concentration of carbon monoxide gas in the room air. The electrochemical sensor cell is based on tin dioxide (SnO²). When this substance comes into contact with carbon monoxide, the conductivity changes through a reaction. Even the smallest change in conductivity and the associated change in resistance is analysed and evaluated by the CO detector. At low CO concentrations, the warning device calculates the time period in which it becomes dangerous for people and triggers the alarm beforehand. There are minimum legal requirements for the time until the alarm is triggered depending on the CO concentration: The alarm levels can usually be found in the product details. Many carbon monoxide detectors also have a pre-alarm that is activated at lower concentrations. This is usually done via a visual signal on the display or via an LED.

How and where exactly do you install your CO detector?

The best way to find out "how" is to refer to the enclosed installation instructions. CO detectors should be installed in the middle wall area in rooms with CO sources as well as in bedrooms and living rooms. You have already learned above what sources of carbon monoxide leakage there may be. CO detectors should be installed in rooms with such sources, in bedrooms and living rooms as well as in fuel stores. The alarm must be audible everywhere, so it is best to think about a wireless carbon monoxide alarm. Especially if you live in a large building. Mount the alarm in the middle to upper wall area at a height of approx. 1.50 to 2.00 m. The display must be easy to see. The display must be easily visible. Keep at least two metres away from CO sources, otherwise there is a risk of a false alarm. It is even more important that you do not install the alarm near windows, doors, extractor bonnets or similar. Fresh air flowing in and draughts in general can greatly falsify the readings. In the worst case, the CO detector will not even trigger the alarm. Other circumstances that can lead to false readings are strong climatic fluctuations and high humidity, such as in showers or bathrooms. If you are unsure, ask a competent dealer for safety technology. If you do not opt for the mobile version, CO detectors are usually fixed to the wall with two screws and dowels. The size of the screws and the depth of the drill holes varies. Fastening with the help of glue, magnets or similar is also possible. For more details, simply refer to the enclosed operating/assembly instructions.

How do you maintain and test your CO detector?

With battery-operated CO detectors, maintenance only consists of changing the batteries and testing. Many CO detectors have a self-check function or at least a test button. However, only a CO detector test device is really reliable. You should service or test your CO detector from time to time. With battery-operated detectors, you do this as soon as the batteries need to be changed. This is not necessary for detectors with lithium batteries, as their service life corresponds to that of the CO alarm. The self-checking function of some CO alarms tests itself and notifies you of malfunctions via the display, an LED or a separate alarm. In the case of devices with a test button, you must perform the test manually. To be on the safe side, you can also get a CO detector test device. This allows you to test whether the CO sensor really reacts when it comes into contact with carbon monoxide gas and sounds the alarm.

What to do in case of a carbon monoxide alarm?

Do not panic! Open the windows and quickly leave the house with your family or other residents. Then dial the emergency number. If the CO alarm goes off, you should react quickly: open the windows. Of course, you should not run through the house in a panic and open every window. This is more about bringing some fresh air into the room you are in. Then leave the house with your family and inform the other residents if they did not hear the alarm. But only as long as you do not endanger yourself. Then dial 112 for the emergency call and wait until the rescue service or the fire brigade has arrived. You must then inform them of your suspicion of carbon monoxide poisoning. It is important that you do not re-enter the room until it has been cleared. Even if the carbon monoxide problem is fixed and it seems safe again, it is of utmost importance that the CO sources are found and appropriate repairs are made!

Image source: / ferarcosn