Kidde 5CO Carbon Monoxide Alarm review
By Tom Calder
A dependable, no-frills carbon monoxide alarm from a well-known brand, Kitemarked to BS EN 50291 with a 10-year sensor. It does the essential job well, though there is no digital readout and you will need to keep the AA batteries fresh.
- Best for
- An affordable, standards-approved CO alarm for a room with a gas boiler, fire or stove.
- Skip it if
- You want a digital display showing live CO levels or a fully sealed battery you never have to…
as of 2 Nov 2026, 16:07 GMT · Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.co.uk at the time of purchase will apply to the purchase of this product.We earn a commission if you buy through the retailer links on this page. It doesn't change our verdict. How we make money →
Researched, not used. We haven't used this product. This review is built from the maker's specifications, owner reports and our own sizing.
What we like
- Kitemarked to BS EN 50291-1 with a 10-year sensor life from a trusted brand
- Inexpensive and widely stocked at UK retailers
- Simple to fit, wall-mounted or freestanding, with batteries and fixings supplied
Worth knowing
- LED indicators only, so you cannot read the actual CO ppm level
- Uses replaceable AA batteries rather than a sealed 10-year cell, so they must be kept charged
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Our review
The Kidde 5CO, sold now as the K5CO, is the plain, cheap carbon monoxide alarm: an electrochemical sensor with a ten-year life, two replaceable AA batteries, an 85dB sounder and three LEDs, Kitemarked to BS EN 50291-1:2018. It does the one job well for the price of a few batteries. You have to change those batteries, and there is no screen.
What the manual says
Kidde's manual for the K5CO and its digital sibling gives two AA alkaline cells with at least a year's life in normal use, an alarm of 85dB or more at three metres, a weekly test button, a hush that silences the alarm for 24 hours and stops working after 30 days, and an operating range of -10 to 45C. The end-of-life signal is an amber LED blinking twice every minute with two chirps; the manual says to replace the alarm ten years after installation. Retailers list the Kitemark to BS EN 50291-1:2018, CE and UKCA marks, and a seven-year warranty; Kidde's manual gives no warranty term itself, so check the box.
Siting, from the same manual: one to three metres horizontally from the appliance, wall-mounted with the top at least 150mm below the ceiling or on the ceiling at least 300mm from any wall, and not in a garage, bathroom, by a vent or within 300mm of a light fitting. Mounting holes are 78mm apart and it can also stand on a shelf.
Why it is worth having, and its catch
The NHS advises an alarm in every room with a gas, oil, coal or wood-burning appliance, and at this price there is no reason not to have one in each. The catch is the batteries. A sealed alarm looks after itself for a decade; this one chirps when the cells run down, and if that happens while you are away or the chirp is ignored, the room is unprotected. Kidde's weekly test button is the discipline that goes with it. English landlords' rules since October 2022 accept battery alarms but the government's guidance recommends sealed-for-life ones, which says something. Our carbon monoxide poisoning symptoms guide covers what to do if it sounds.
How it compares
On the carbon monoxide alarms page, Kidde's own 5DCO adds a digital readout updated every 15 seconds in the same body, for a little more. The FireAngel FA3820 and Aico Ei208 are the sealed ten-year alarms that remove the battery question. The FireAngel FA3322 is sealed and has a screen. The X-Sense CO03D is the cheap digital alternative. The Kidde 5CO is the one to buy several of for a house with a boiler, a stove and a gas hob, provided someone will change the batteries; our Aico vs Kidde guide weighs the brands.
Our verdict
Buy it as the low-cost way to put a Kitemarked alarm in every appliance room, and put a battery change in the calendar with the clocks going back. Skip it if you want a reading, or if nobody in the house will remember the batteries; a sealed ten-year alarm costs a little more and asks nothing.
A researched review, built from the maker's specs, manual and UK listings; facts checked 2 Nov 2026. Sources: Kidde: K5CO and K5DCO carbon monoxide alarm user guide (ManualsLib copy); B&Q: Kidde K5CO 10-year life carbon monoxide alarm, Kitemark and warranty listing (read 2 November 2026); NHS: Carbon monoxide poisoning; GOV.UK: The Smoke and Carbon Monoxide Alarm (England) Regulations, Q&A booklet.
Who shouldn't buy this
You want a digital display showing live CO levels or a fully sealed battery you never have to touch, in which case the digital 5DCO or a sealed-battery model suits better.
Key specs
| Standard | BS EN 50291-1, Kitemarked |
| Sensor life | 10 yr |
| Display | LED only (no digital readout) |
| Power | 2 x AA (replaceable, supplied) |
This is a Researched review: we haven't used this product. We check every specification against at least two independent sources, re-check the UK price on a schedule where we can track it automatically, and say plainly who it isn't for. Commissions never change a rating.
If this isn’t the one
Best for Bedrooms and living rooms wanting a clear, readable CO alarm with no battery faff
as of 2 Nov 2026, 16:07 GMT · Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.co.uk at the time of purchase will apply to the purchase of this product.
Best for Households with a gas boiler, hob, open fire or wood burner who want fit-and-forget protection.
as of 2 Nov 2026, 16:07 GMT · Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.co.uk at the time of purchase will apply to the purchase of this product.
Best for A home rewiring or new build where CO alarms are fitted on the mains circuit.
as of 2 Nov 2026, 16:07 GMT · Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.co.uk at the time of purchase will apply to the purchase of this product.Questions
How long do the batteries last in the Kidde 5CO?
Kidde's manual says at least a year in normal use from two AA alkaline cells. The alarm chirps when they run low, and the sensor itself lasts ten years from installation.
Is the Kidde 5CO Kitemarked?
Retailers list it as Kitemarked to BS EN 50291-1:2018, with CE and UKCA marks. Kidde's manual does not print a Kitemark number, so look for the mark on the alarm itself.
Where should the Kidde 5CO be fitted?
One to three metres from the appliance, wall-mounted with its top at least 150mm below the ceiling or on the ceiling 300mm from walls, and not in a bathroom, garage, by a vent or within 300mm of a light, per Kidde's manual.
Does the Kidde 5CO show the CO level?
No. It has three LEDs for power, fault and alarm. Kidde's 5DCO is the same alarm with a digital readout.
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