Best carbon monoxide alarm UK: a pick for each job
Updated: 20 October 2026
You have a boiler cupboard and a list of best alarms, and the model they crown is not one of the twelve amazon.co.uk listings in this comparison. The best carbon monoxide alarm UK shoppers can take from this shelf matches one job: the most reviews, a printed Kitemark with a sealed cell, or a screen. This page says who each is for, and who should leave the about £3.42 box. Prices sit on the [CO detector comparison](/hub/fire-protection/co-detector). Figures are the 19 October 2026 capture: we ran no gas test, and a qualifying purchase can earn us a commission at no extra cost to you.
You have a boiler cupboard and a list of best alarms, and the model they crown is not one of the twelve amazon.co.uk listings in this comparison.
You have a boiler cupboard and a list of best alarms, and the model they crown is not one of the twelve amazon.co.uk listings in this comparison. The best carbon monoxide alarm UK shoppers can take from this shelf matches one job: the most reviews, a printed Kitemark with a sealed cell, or a screen. This page says who each is for, and who should leave the about £3.42 box. Prices sit on the CO detector comparison. Figures are the 19 October 2026 capture: we ran no gas test, and a qualifying purchase can earn us a commission at no extra cost to you.
Our top picks
| Badge | Product | Standard on the listing | Battery | amazon.co.uk reviews | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Kidde Kidde 5CO | None printed | AA, life not stated | 4.7 from 59,540 | 6.3 | about £13.75 | View offer |
| Alternative |  X-Sense X-Sense XC0C-SR | EN 50291, no year | 2 × AA, 3-year claim | 4.7 from 6,311 | 7.5 | about £15.98 | View offer |
 FireAngel FireAngel FA3820 | Kitemark, BS EN 50291-1:2018 | Sealed 10 years | 4.6 from 3,466 | 9.4 | about £22 | View offer |
On this page
What best can mean in this set
These listings were not asked the same question, so one winner would be a fiction. One has tens of thousands of reviews and no standard number. One prints a BSI Kitemark and a sealed ten-year cell. Best, here, means the listing that matches your job.
Review volume points at the Kidde 5CO. A Kitemark and a sealed cell point at the FireAngel FA3820. A number you can read points at a display. The FireAngel FA6813 at about £13.98 is the best-value card on the main comparison: electrochemical, both standard years printed, and not for a Scottish home that needs a sealed cell.
Kidde 5CO when review volume matters
The Kidde 5CO (B07WSX4NCV) is the top pick when you are buying other people's record of living with the alarm. On 19 October 2026 it was about £13.75, rated 4.7 from 59,540 reviews. It suits an England or Wales shopper who will change AA cells and can live with a listing that names no standard.
The standard field is blank, and a spec line says photoelectric, which is smoke-alarm language, while reviews talk about AA cells you replace. We did not open a unit to see which line is the sensor. Leave it for a Scottish home that needs a sealed long-life cell, and read how that duty differs by nation on the carbon monoxide alarm landlord rules page.
FireAngel FA3820 when the listing must show a Kitemark
The FireAngel FA3820 (B0B9HC17ZG) is the listing when the amazon.co.uk text has to show the paperwork. At about £22, with 4.6 from 3,466 reviews, it states an electrochemical sensor, a sealed ten-year lithium cell, BSI Kitemark KM 551504, and both BS EN 50291-1:2018 and BS EN 50291-2:2019. One review says this alarm faulted after two years and the cell could not be changed. Choose it for the printed Kitemark and the sealed cell, including a Scottish home where that battery shape is the point, and skip it if you need a ppm readout or a lower price.
A screen, if you want a number
A display is for when you want a concentration, not only a siren. The Kidde 7DCOC (B00ABGEL62) was about £18.25, rated 4.7 from 6,393 reviews, with a continuous display and three AA cells, and the amazon.co.uk capture prints no standard number. A TLC datasheet for order code 7DCOC claims BSI approval to EN 50291:2010, parts 1 and 2. That older claim stays on the datasheet and is not a certification of the live listing.
The other screen is the X-Sense XC0C-SR at about £15.98, rated 4.7 from 6,311 reviews, with peak memory and AA cells claimed for three years. It prints EN 50291 with no year. Use a screen to watch a figure in the hour after a boiler service. A touring caravan is a different part of the standard, on the carbon monoxide alarm for caravans page.
Who should skip the about £3.42 EiBEST
The EiBEST AW-D125S at about £3.42 is the listing to skip when you want an alarm you can leave on the wall. It was rated 4.1 from 290 reviews, and those reviews cite cells lasting about a week. The listing also claims an immediate alarm at 100 ppm. That sentence is not a measurement from this desk, and it does not add a Kitemark. The 5CO is for England or Wales if you will change AAs and accept a blank standard. The FA3820 is for a printed Kitemark and a sealed cell, unless you need a screen.
Common questions
Is the most-reviewed alarm the one to buy?
Only if review volume is the job. The Kidde 5CO has 59,540 reviews at 4.7, at about £13.75, and that record does not fill the blank standard or correct the photoelectric spec line. Buy it in England or Wales if you will change AA cells. Leave it when you need a Kitemark on the listing, or a sealed cell for a Scottish home.
Who should buy the FA3820 instead?
Buy the FA3820 at about £22 for Kitemark KM 551504, both the 2018 and 2019 parts, and a sealed ten-year cell on the listing. That shape fits a Scottish sealed-battery rule. Skip it for a ppm display, or if a fault would leave you unable to swap the cell. One review describes a failure at two years.
Which listing if I want to see a ppm number?
The 7DCOC at about £18.25 has a continuous display and three AA cells, and the listing prints no standard. The X-Sense XC0C-SR at about £15.98 adds peak memory and prints EN 50291 with no year. The 2010 datasheet claim, and the later K7DCO, are not this live listing. Neither screen is a sealed Kitemark alarm.
Why skip the about £3.42 alarm?
Reviews cite cells lasting about a week, so about £3.42 is not a ten-year cost. The immediate alarm at 100 ppm is a listing claim, not a result from our desk, and the page shows no Kitemark. Which?'s sub-£10 pattern is context, not a Don't Buy label for this ASIN.
Does a Which? Best Buy in the search results mean that model is here?
FireAngel says the FA3322 is the Which? Best Buy from November 2024. That model is not in this set, so the badge does not transfer to the 5CO or the EiBEST. The line about the FA3820 detecting carbon monoxide is the maker's account, not a test we ran.
Is a sealed battery on the XINDUM CO12 the same as a Kitemark?
No. The CO12 is sealed at about £14.43 and prints no Kitemark. A sealed cell answers a battery question, while KM 551504 on the FA3820 is a mark on the page. Leave the CO12 out of the Scottish job that needs that mark.
Related pages
Sources
Public UK sources and the FireAngel FAQ, last checked on 19 October 2026.
- The Smoke and Carbon Monoxide Alarm (England) Regulations 2015, regulation 4 (retrieved 19 October 2026)
- GOV.UK smoke and carbon monoxide alarm Q&A for landlords (retrieved 19 October 2026)
- Approved Document J divisional circular on alarm amendments (retrieved 19 October 2026)
- Scottish Government tolerable standard, fire and carbon monoxide detection (retrieved 19 October 2026)
- mygov.scot home fire safety (retrieved 19 October 2026)
- Renting Homes (Fitness for Human Habitation) (Wales) Regulations 2022, regulation 5 (retrieved 19 October 2026)
- NHS carbon monoxide poisoning (retrieved 19 October 2026)
- FireAngel homeowner FAQs (retrieved 19 October 2026)