Where to put a carbon monoxide detector to stay safe at home

Here’s everything you need to know about carbon monoxide detectors – from where to place them in your home to how to test they’re working properly.

What is carbon monoxide?

Carbon monoxide (CO) is a colourless, odourless, and tasteless gas that’s extremely toxic and can even be deadly if inhaled in high levels. It’s sometimes called the ‘silent killer’ because you can’t see or smell it, but it can build up quickly in enclosed spaces without any obvious warning signs.

It’s commonly produced by gas appliances that aren’t working correctly, like boilers, cookers, fires, or heaters. If these appliances don’t burn fuel as they should, they can release carbon monoxide into your home.

What is a carbon monoxide detector, and what does it do?

Since carbon monoxide is extremely difficult to spot, the best way to protect your home is with a carbon monoxide detector. These small devices work similarly to smoke detectors; they sense if CO is present in your home and warn you before it reaches harmful levels.

They’re usually mounted on walls or ceilings and use special sensors to detect carbon monoxide in the air. If the gas starts to build up, the detector sounds a loud alarm to alert you and your family, giving you time to act and stay safe.

There are a few types of carbon monoxide detectors available, each with different power sources and features:

• Single-use battery detectors – These come with batteries sealed inside and are designed to work for a fixed lifespan (anywhere from 5–10 years) before you replace the entire unit. 

• Replaceable battery detectors – These allow you to swap out the batteries when they run low, helping your detector keep working without replacing the whole device. The batteries will need to be replaced every 2–3 years.

• Plug-in detectors – These plug straight into a mains socket, and may also have a battery backup in case of power cuts. 

• Smart carbon monoxide detectors – Like smart meters, these connect to your phone or smart home system, sending alerts remotely so you can stay informed if there’s a leak even when you’re not at home. Learn more about how smart meters work here.

Whichever type of detector you have, it’s an essential part of upping the safety of your home. In 2024, nearly half of homes in the UK (42%) didn’t have a carbon monoxide detector alarm installed.

Where to put a carbon monoxide detector in your home

Knowing exactly where to place your carbon monoxide detector is key to making sure it can do its job properly. Since carbon monoxide is slightly lighter than air, the detector should be placed at a height of 150cm or more.

Here’s where you should put your carbon monoxide detectors:

1. Place a carbon monoxide detector in every room in your home that has a fuel-burning appliance installed.

2. Position the alarm between one and three metres horizontally from the appliance for the best detection accuracy. 
   a. If fixed on a wall, it should be above the appliance and 15cm below the ceiling. 
   b. If installed on the ceiling, it’s recommended that the alarm is at least 30cm away from any wall.
   c. A CO alarm can also be unfixed to a structure, but should be at head height, like on a bookcase or table.

3. Make sure there’s at least one alarm on each floor of your home to provide full coverage.

4. Place it near bedrooms or sleeping areas so you can hear the alarm while you sleep.

5. Avoid putting detectors near windows, vents, extractor fans, or doors where fresh air could stop carbon monoxide from reaching the sensor.

6. Don’t place the alarm near any appliance that produces flames, like a fireplace or gas stove.

Your alarm will come with the manufacturer’s instructions, so it's crucial to read their guidance on the best place to put a carbon monoxide detector.

Are carbon monoxide detectors required by law?

In October 2022, the UK Government enforced new regulations that stated that in England, Scotland, Wales, and Northern Ireland, landlords must install carbon monoxide detectors in any room with a fixed combustion appliance. These include gas boilers and heaters, and apply to all rented properties, whether privately rented or social housing.

Although a carbon monoxide alarm isn’t currently a legal requirement for homeowners, it’s strongly recommended for safety. If you have any fuel-burning appliances in your home, installing detectors is one of the simplest ways to protect your household.

The regulations also specify that alarms should meet the British Standard BS EN 50292:2023  and be properly maintained to ensure they work when you need them.

How many carbon monoxide detectors do I need?

The number of carbon monoxide detectors you need depends on the size and layout of your home and where your fuel-burning appliances are located.

As a general rule:

• You should have at least one detector on every floor of your home to make sure you’re covered no matter where you are.

• You should place a detector in every room that contains a fuel-burning appliance, like boilers or gas heaters.

• You should also consider installing detectors near bedrooms or sleeping areas.

For larger homes or properties with multiple appliances, you might need more detectors to ensure complete coverage and early warnings.

What to do if a carbon monoxide alarm goes off

If your carbon monoxide alarm sounds, it’s important to act quickly and safely. In this situation, NHS guidance recommends that you:

1. Immediately stop using any appliances, turn them off, and open all doors and windows to let fresh air into your home and help clear the gas.

2. Leave the property and go outside.

3. Call the National Gas Emergency Service on 0800 111 999 to report the alarm and get advice on next steps.

4. Do not go back into the building until it’s safe to do so.

If you don’t feel well and start to suffer from headaches, nausea, or dizziness, seek medical attention straight away by contacting your doctor or calling 999 in case of an emergency.

How to test a carbon monoxide alarm and know if it’s working

Test your alarm once a month by pressing the test button on the device. It should be visible on your alarm, but it’s best to read the instruction manual and follow the manufacturer’s guidance on how to test your CO detector. You should hear a loud beep or see a flashing light to confirm it’s working.

If your alarm uses replaceable batteries, check the batteries regularly. Change them when you hear a warning beep or at least once a year. For alarms with sealed, long-life batteries, replace the entire unit when it reaches the end of its lifespan.

It’s also strongly recommended that you have your boiler and other fuel-burning appliances serviced annually by a Gas Safe-registered engineer, as this can catch any issues early and help reduce the risk of carbon monoxide leaks before they occur.

How long does a carbon monoxide alarm last?

Most carbon monoxide alarms are designed to work effectively for around 5–10 years, depending on the make, model, and type of detector. While the sensor’s lifespan can be up to 10 years, the alarm’s battery may need to be replaced sooner.

Newer alarms will also have a built-in warning, like a beeping sound, to tell you when the unit has reached the end of its lifecycle and it’s time to replace it.

Once you hear the warning sound, replacing the detector is vital as the sensors can become less reliable over time.

What other gases can set off a carbon monoxide detector?

CO detectors are specifically designed to sense carbon monoxide gas, so other gases shouldn’t trigger them, but there are some cases where other factors might cause a false alarm. These include:

• Hydrogen gas from charging batteries

• Certain aerosol sprays

• High levels of humidity or steam from showers or cooking

• Dust or dirt buildup on the sensor

• Strong paints

Because of these factors, the positioning of your CO detector is crucial to reduce the chances of a false alarm.

Simplify your home energy with UW

With the right detectors in place, you can protect your home from the dangers of carbon monoxide. Just remember to install them in the right places, test them regularly, and know what to do if the alarm sounds.

At UW, we’re here to help you take care of your home – from energy and broadband to mobile services – all bundled together on one easy-to-manage bill.