Where to place a carbon monoxide detector, and how it works

26 October 2021 | Celia Topping

Carbon monoxide is called the silent killer, because you can’t see it, smell it, hear it, or taste it. The only way to know it’s present is by using a carbon monoxide detector. 

In this article we’ll explain all about carbon monoxide, how to find the right detector to buy, and where to place it for maximum effectiveness. 

Click on the links below to find the section you need. 

What is carbon monoxide, and how is it produced?

What does a carbon monoxide detector do?

Where to place a carbon monoxide detector

Where can I buy a carbon monoxide detector?

How do I check my carbon monoxide detector?

What is carbon monoxide, and how is it produced?

Carbon monoxide is a highly toxic gas. It’s produced by the incomplete burning of fuels such as gas, oil, wood and coal. Breathing it in, even for a short time, can cause serious organ damage, and even death. Any appliance that burns fuel can produce carbon monoxide. This includes heaters, oil-fired boilers, car engines, and fires.

For further information on how to spot carbon monoxide poisoning and how to stay gas safe, read our guide. 

What does a carbon monoxide detector do?

Carbon monoxide detectors work in a similar way to smoke or fire alarms – they sound an alarm when carbon monoxide is detected in the air. It will go off before you even start sensing symptoms. 

If there’s fairly low carbon monoxide levels, around 50 parts per million (ppm), it could take up to 8 hours for the detector to sound an alarm. Higher levels (over 150ppm) can set it off within minutes1

These are the 3 different types of carbon monoxide detector, that work in different ways:

  • Biomimetic sensor: a gel inside the alarm changes colour when it absorbs carbon monoxide. This colour change sets off the alarm. (Cheaper carbon monoxide patches that also change colour are available – but they don’t have an audible alarm, so we don’t recommend them.)
  • Metal oxide semiconductor: when these gadgets detect carbon monoxide, it causes an electrical change in the circuit, which trips the alarm. 
  • Electrochemical sensor: these alarms contain a chemical solution, with electrodes that can sense a change in electrical currents when carbon monoxide is present. This change triggers the alarm. 

Will a carbon monoxide detector detect a gas leak? 

No. Your carbon monoxide detector will only sound the alarm when it detects carbon monoxide. It can’t detect any other sort of gas. 

If you think you can smell gas, follow the emergency guidelines here. But when it comes to gas leaks, think prevention, not cure: get yourself a gas detector too! 

What other gases can set off a carbon monoxide detector?

In a word, none! 

Can smoke detectors detect carbon monoxide? 

Absolutely not! They detect entirely different things. A smoke alarm won’t alert you to a carbon monoxide leak, and a carbon monoxide detector won’t alert you to smoke. To be safe, you need to install both. 

Do you need a carbon monoxide detector with oil heat?

If your home is heated with oil, there is less of a risk of carbon monoxide poisoning. But it isn’t impossible. It’s always best to err on the side of caution, and still install a carbon monoxide detector. Even a slight chance can mean the difference between life and death. 

Do I need a carbon monoxide detector?

Yes! If you have a gas appliance in your home, you need a carbon monoxide detector. Considering around 85% of British homes use gas, it’s likely you do. 

Around 60 people in the UK die every year from carbon monoxide poisoning2, and many more suffer long-term organ damage. A detector is a vital bit of kit to protect you and your family against this risk.

Is carbon monoxide lighter than air?

Yes, carbon monoxide is actually slightly lighter than air. It can also be found within warm, rising air. For this reason, detectors should be installed at 5 feet or above.  

Where to place a carbon monoxide detector

Carbon monoxide detectors save lives. Knowing where to install these detectors is vital to protect you and your family against this poisonous gas. 

  • Put a detector in every room that contains a fuel-burning appliance, or in a central location, such as a hallway or a landing. 

  • If you’re only installing one detector, put it near your bedroom so you’ll definitely hear it if you’re asleep.

  • Don’t place the detector near a fireplace, or any appliance that produces flames (like your gas hob).

  • Make sure the alarm is at least a metre away from fuel-burning appliances, such as boilers and ovens.

  • Place the alarm at head height, around the level you breathe. It doesn’t have to be fixed on a wall – you could place it on a table, shelf, or bookcase. Ideally it should be around 15cm from the ceiling.

  • Don’t put it in cupboards, behind furniture, or near outside doors or ventilation equipment (such as extractor fans). This will stop it from working properly.

  • Keep the alarm away from areas where you get a lot of condensation, such as bathrooms, or next to cookers.

  • Test the alarm regularly, just as you would with a regular smoke alarm. Replace the batteries as soon as the low-battery signal beeps.

  • Always read and follow the manufacturer’s instructions when placing, testing, and servicing the alarm. Pay close attention to any notes on its battery life, and when batteries should be replaced.

    For more information on gas safety and detecting gas leaks, or what to do in a gas emergency, check out our comprehensive guides. 

    How do I install my carbon monoxide alarm?

    You’ve made the first important step in protecting yourself, by buying a carbon monoxide detector. But installing it in the right place is just as important. Happily, installation is a simple DIY task – it could be as easy as just putting it on a high shelf. 

    Simply follow the manufacturer’s instructions. They should give clear guidance about placing, testing, servicing, and replacing the detector. Pay careful attention to information about battery life, and when batteries should be replaced. A detector with a flat battery won’t save your life. Most detectors last around 5 to 7 years, but some will do the job for as long as 10 years. 

    There are some unsafe detectors out there – so do your research and make sure yours is reliable. Brands such as Fire Angel and Honeywell are reputable companies – but any that comply with the BSEN50291 manufacturing standard are safe to use. 

    What do carbon monoxide detectors look like?

    carbon monoxide detector

    Look for a small off-white rectangular box, with “carbon monoxide alarm” printed on the front. Compared to smoke alarms, they’re quite different in shape, as smoke detectors are usually round. 

    How many carbon monoxide detectors do I need?

    This depends on the size of your home. We recommend that you get a carbon monoxide detector for every level of your home, as well as outside bedrooms. This includes the basement and the garage if you have fuel-burning appliances. 

    Should my landlord provide a carbon monoxide detector?

    Absolutely! They should provide you with as many carbon monoxide detectors as you need, referring to the advice given above. 

    Are carbon monoxide alarms required by law? 

    According to The Smoke and Carbon Monoxide Alarm Regulations (2015), landlords must give their tenants carbon monoxide detectors for any room that uses solid fuel. They also must make sure the alarms are in good working order at the start of each tenancy. 

    The regulations recommend that landlords provide carbon monoxide alarms in rooms with gas appliances too.

    Where can I buy a carbon monoxide detector?

    Carbon monoxide detectors are available at most DIY stores or online. There are many different types, but go for one that makes a sound, so you’re alerted to a leak straight away. The patch detectors, which change colour when a leak is detected, are useless if a leak occurs while you’re asleep. 

    Reliable detectors cost £20 or more. This article by Which? offers guidance on making the right choice.  

    Make sure your detector complies with the BS50291 standard, and has a British or European Kitemark.

    What are the different types of carbon monoxide detectors?

    There are 3 main types of carbon monoxide detectors. Remember, don’t be tempted to get a cheap one, it’s always better to be safe than sorry! 

    • Sealed battery carbon monoxide detectors – this type of detector has the battery sealed inside the unit. You can’t change the battery. The alarm will beep to let you know when you need a new unit. This type of alarm can last for up to 10 years – and not needing to change the battery for 10 years is a real bonus for busy households!

    • Replaceable battery carbon monoxide detectors – the batteries will need replacing every 2 to 3 years in this kind of alarm. Although this type of detector is cheaper than sealed battery detectors, buying the replacement batteries will push the price up. These detectors last between 5 and 10 years.

    • Smart carbon monoxide detectors – if you live a smart life through your phone, this is the one for you. Not only does the alarm sound, but you also get an alert through your phone. This could be useful if there’s a carbon monoxide leak while you’re not at home. These alarms cost around 4 times as much as sealed battery detectors, and they’ll last between 7 and 10 years. 

    How do I check my carbon monoxide detector?

    Be sure to keep the instruction manual when you buy your detector, as it’ll have all the information you need that’s specific to your alarm. Usually there’s a test button to press, which is easy to find. 

    If you hear a low battery signal, you must either replace the batteries or buy a new carbon monoxide detector. Again, to find out which you need to do, read the instruction manual.  

    How often should carbon monoxide detectors be checked? 

    Test the detector at least every month, and ideally every week. Make sure you replace the batteries when instructed to do so in the manual. 

    Should I follow any safety tips for using and maintaining my carbon monoxide alarms?

    The safest thing you can do is follow the manufacturer’s instructions included in the box. Keep this booklet in a safe place for future reference. Never take out the battery to use in another device – the likelihood is you’ll forget to replace it. 

    Carbon monoxide detector beeping – what does this mean? 

    Beeping generally means the batteries need replacing, or the detector has come to the end of its life. Either way, you need to take immediate action. Read the instruction manual to find out what the beeps mean, and don’t delay carrying out the instructions. 

    What do I do if my carbon monoxide detector goes off?

    Be sure you know the difference between the alarm going off because of carbon monoxide, and the “flat battery” or “end of life” alarm. Read the instruction manual, which will describe the different alarm sounds. 

    1. Don’t panic. Gather everyone in your home together and move outside immediately. Open the windows and doors on your way to the exit, but don’t go out of your way to open others in the house. 
    2. Check everyone’s health. Any flu-like symptoms could suggest poisoning. For more information, check our carbon monoxide poisoning guide. 
    3. If you notice any symptoms, call 999 straight away.
    4. Do not re-enter your home until the alarm stops ringing or emergency responders say that your home is safe.
    5. Contact a professional to test every fossil fuel-burning appliance in your home, plus any other possible source of carbon monoxide to prevent a future incident.

    Acting quickly is essential if your alarm goes off, because low doses of carbon monoxide over long periods can be just as dangerous as sudden exposure in ultra-high doses.

    Find out more about the signs of carbon monoxide and the symptoms of carbon monoxide poisoning in our guide to carbon monoxide safety: how to spot carbon monoxide poisoning.

Sources and references



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