Carbon monoxide is the hazard you can't see, smell or taste, and UK winter is when it bites: boilers, gas fires, wood burners and stoves are all running, windows are shut, and a blocked flue or a badly serviced appliance can fill a room without anyone noticing. A CO alarm is a cheap piece of plastic that does one job — it goes off before the gas that's making you sleepy becomes the gas that doesn't let you wake up. Every home with a fuel-burning appliance should have one, and it is not the same device as a smoke alarm.
The decisions are simple. A sealed 10-year alarm is the sensible default: you fit it and forget it, with no battery to change or forget, and the whole unit is replaced when the sensor reaches end of life (CO sensors do wear out, which is why alarms have an expiry date). Look for the EN 50291 standard and ideally a BSI Kitemark. From there it's about how it's powered and how clever you need it: mains models for a permanent fixture, combined smoke-and-CO units to cover two hazards from one spot, and Wi-Fi models that alert your phone when you're out — useful if you're keeping an eye on an older relative's house.
Our picks span that range: a fit-and-forget sealed 10-year alarm, a mains-powered model, two combined smoke-and-CO units (one with Wi-Fi alerts), a recognisable-brand budget 10-year alarm, and a simple digital-display everyday pick. Fit one near each fuel-burning appliance and outside sleeping areas, at roughly head height or as the maker specifies — not on the ceiling directly above a boiler — test it monthly, and never treat a chirping low-battery or end-of-life warning as background noise.
