We use cookies to allow us and selected partners to improve your experience and our advertising. By continuing to browse you consent to our use of cookies. You can understand more and change your cookies preferences here.


When you click on a retailer link on our site, we may earn affiliate commission to help fund our not-for-profit mission.Find out more.

1 Jul 2020

5 things you need to know when buying a CO alarm

What to look for if you're buying a carbon monoxide alarm, the lowdown on CO and summer holidays, plus the alarms to avoid

With high street shopping now possible as we emerge from the coronavirus lockdown, we share the key things to look for when choosing a carbon monoxide (CO) alarm, whether you're buying in person or online.

Which? tests over the last four years have shown that not all CO alarms can detect the deadly gas reliably and repeatedly, with some completely failing at the one task they're designed to do.

Read on for five key things to look for to give you the best chance of buying an alarm that you can rely on. Plus we show you the carbon monoxide alarms to avoid and some things to consider if you're taking a break this summer.

Jump straight to our carbon monoxide alarm reviews to see our recommended models.

1. Pick a recognisable brand of carbon monoxide alarm

A rule of thumb to follow is to go for a brand that you recognise when buying a carbon monoxide alarm. That way you give yourself a good chance of finding an alarm you can trust.

Almost all of the carbon monoxide alarms that have failed our tests over the last four years have been unbranded products. They're typically made in China and claim to meet the requirements of the CO alarms standard. But in our tests they simply failed to detect CO when we needed them to.

Read our carbon monoxide alarm reviews to see the brands you can trust.

2. Expect to pay more than £10

If you head online or to the shops thinking that you'll get a decent CO alarm for less than £10, you could end up disappointed or worse. Most of the CO alarms that have failed to detect the killer gas in our lab tests have been on sale for less than a tenner.

So, when looking for a CO alarm for your home and to protect your family, look to pay £10 or more. Many of the good alarms that we've tested cost between £10 and £25, with the difference in price caused by things like some alarms having digital displays.

If you're looking for a smart carbon monoxide alarm, expect to pay more. Smart alarms will sound the alarm in your home and on your phone, which could be a lifesaver if there was a build-up of the gas in your home while you were out.

The smart Nest Protect Smoke + CO Alarm does both detection jobs in a connected way and costs around £89.

3. Buy from the high street or from online retailers you trust

Research we have carried out over the years shows that high street retailers and their online equivalents tend to only stock carbon monoxide alarms from well-known and recognisable brands. So, if you were shopping at a DIY chain or in a supermarket, we think the odds are good that you will end up with a brand of alarm that sounds when you need it to.

But not every model from every well-known brand of carbon monoxide alarm has passed all of our lab tests. One alarm from a renowned manufacturer failed to detect the gas in one of our lab assessments.

It's among the 10 Don't Buy carbon monoxide alarms to avoid on our site right now.

4. Avoid patch-style carbon monoxide detectors

Carbon monoxide detectors featuring a circle in the middle of a patch will change colour in the presence of CO. But that's all they do. The product detects CO but it's not an alarm and it won't be able to protect you while you sleep and at other times when you're not looking directly at it.

The safest option is to avoid this kind of product and instead choose an alarm with a proven track record of detecting the gas and that will audibly alert the household in an emergency.

5. Be careful when buying carbon monoxide alarms from online marketplaces

It's true to say that you'll be able to find carbon monoxide alarms from reliable brands on online marketplaces, there's no doubt about that. But equally, these are the sources through which many dangerously unreliable alarms are sold.

Seven CO alarms that failed our detection tests were bought through sellers on online marketplaces in the last year. So if you're dead set on buying from an online marketplace, go for a new product from a recognisable brand rather than a cheap and unbranded alternative.

Rogues gallery: the dangerous carbon monoxide alarms to avoid

If the carbon monoxide alarm in your home looks like one of those below, you should replace it with a Which? Best Buy alarm as soon as you can.

Going on holiday and carbon monoxide alarms

Landlords and owners of holiday cottages or river boats in the UK are required to install and check carbon monoxide alarms in any room where solid fuel is burned, such as a living room with a log burner. So check that there is an alarm installed when you arrive.

The rules will vary in other parts of the world, so to keep yourself safe, you may want to pack your carbon monoxide alarm and take it with you the next time you travel and stay in private accommodation. Most carbon monoxide alarms will be battery powered and freestanding, which means they won't need to be attached to the wall. If this is the case with yours, it will just be a matter of picking it up and popping it in your bag before you leave.

When you get to your destination, place the alarm high up in the same room as the potential source of carbon monoxide (a fire, a cooker or a boiler), around 15 cm from the ceiling and at least one metre away from boilers, cookers and fires. But make sure it's not directly above a source of heat or steam.

Find out how to identify carbon monoxide symptoms.