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

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.

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, which 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. 

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. 

What else can set off a carbon monoxide detector?

Carbon monoxide detectors can be set off by car engines, cooking appliances, aerosols, strong paints and other gases, so choosing the right location is key.

Can smoke detectors detect carbon monoxide? 

Sadly not, they detect 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?

If you have any sort of gas appliance in your home, you do need a carbon monoxide detector. Around 85% of British homes use gas, which means it’s likely that your home does too. 

Roughly 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 1.5 metres or above.  

Where to place a carbon monoxide detector

Knowing where to install these detectors is vital to protect you and your family against this poisonous gas. Here’s where they need to go:

• 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. It doesn’t have to be fixed on a wall – you could place it on a table, shelf, or bookcase. Ideally it should be at least 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.

How do I install my carbon monoxide alarm?

The manufacturer’s instructions should give clear guidance about placing, testing, servicing, and replacing the detector. 

Follow the instructions that came with your detector, but these are the usual steps:

1. Try to install it at least a metre away from a flame or fuel source to avoid false alarms. You can mount the device on the wall at head height from the ground, but it doesn’t have to be mounted. On a shelf is fine too. Some detectors plug directly into an outlet.

2. Trace and drill holes and hang the mounting bracket.

3. Use fresh batteries. Pay careful attention to information about battery life, and when batteries should be replaced – a detector with a flat battery won’t be able to save lives. Most detectors last around 5 to 7 years, but some will do the job for as long as 10 years. 

What do carbon monoxide detectors look like?

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?

Yes, they should make sure you have 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 in England 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.

In Scotland and Northern Ireland, the law requires a carbon monoxide detector when a new or replacement appliance is installed. But this doesn’t include appliances only used for cooking.

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 around £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: 

• 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.
• 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 less costly than sealed battery detectors, you’ll need to buy the replacement batteries. These detectors last between 5 and 10 years.
• Smart carbon monoxide detectors – if you like smart devices synced to 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 can 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?

Usually there’s a test button to press, which is easy to find. It’s really important to hold on to the instruction manual when you buy your detector. It’ll have all the information you need that’s specific to your alarm, including how to test it. 

And, if you ever hear a low battery signal, you’ll need to 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?

It’s a good idea to test the detector at least every month, or ideally every week. 

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 these in a safe place for future reference. And avoid taking out the battery to use in another device – in case you accidentally 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 action straight away. Either replace the batteries, or check the instruction manual if you’re not sure what the beeps mean. 

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

Here’s what to do: 

• Don’t panic. Turn off all gas appliances if possible. Gather everyone in your home together and go outside immediately. You can open windows and doors on your way to the exit, but the most important thing is to leave.
• Check everyone’s health. Any flu-like symptoms could suggest poisoning. For more information, check the NHS guidance on carbon monoxide poisoning. 
• If you notice any symptoms, call 999 straight away.
• Do not re-enter your home until the alarm stops ringing or emergency responders say that your home is safe.
• 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. Low doses of carbon monoxide over long periods can be just as dangerous as sudden exposure in ultra-high doses.

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. 

Sources and references

¹ https://www.safewise.com/home-security-faq/carbon-monoxide-detector/

² https://www.nhs.uk/conditions/carbon-monoxide-poisoning