Where to Put Carbon Monoxide Detectors in Your Home
CO alarms are not smoke alarms — you need both. A smoke alarm will not detect carbon monoxide.
Carbon monoxide is a silent killer — odourless, colourless, and produced whenever gas, oil, or solid fuel burns incompletely in your home. Faulty boilers, blocked flues, and poorly maintained gas appliances are common culprits, and the problem can affect anyone with central heating, a gas cooker, or a fireplace. Most UK homeowners dramatically underestimate how many CO alarms they need, and many don't realise that positioning matters just as much as having them at all. This guide walks you through everything you need to know about placing CO alarms correctly, testing them regularly, and understanding your legal obligations — whether you're a homeowner or landlord. If you suspect a CO leak or your alarm goes off, leave the property immediately, call the Gas Safe Register's emergency number, and have a qualified engineer inspect your appliances before you return.
Not sure if this matches your problem?
Use our interactive tool — answer a few questions and get a personalised diagnosis.
Most likely cause & what to check
Buy a CO alarm certified to EN 50291 — look for the kitemark on the packaging. Cheap alarms that don't carry this certification may not be reliable.
Place at least one CO alarm on every floor of your home. If you have a boiler, gas fire, or any gas appliance, place an alarm in that room or the room next to it.
Mount alarms at head height (roughly 1–1.5m from the floor) or on the ceiling. CO is roughly the same density as air, so it disperses throughout the room rather than rising or sinking.
Do not place alarms directly above or near gas appliances, in garages, or in very humid rooms — this can cause false alarms.
Place an alarm in or near bedrooms, especially if you have a gas fire or boiler in an adjacent room. CO incidents are most dangerous at night when you're asleep.
Test the alarm monthly by pressing the test button. Replace the battery annually. CO alarms have a lifespan of 7–10 years — check the manufacturer's date and replace accordingly.
Fitting CO alarms is now a legal requirement for landlords in England, Scotland, and Wales in any room with a fixed combustion appliance.
Prefer to have it done for you?
Find me an engineer →🛠 Tools & materials you may need
🔗 Some links above are affiliate links — if you buy through them we earn a small commission at no extra cost to you. This keeps the site free.
Was this guide helpful?
Frequently asked questions
How do I know if I have a carbon monoxide problem?
Symptoms include headaches, dizziness, nausea, and chest pain that improve when you leave the house — though these can mimic flu, so don't rely on them alone. The only reliable way to detect CO is with a certified alarm; if yours sounds, evacuate immediately and call the Gas Safe Register's emergency line (0800 408 5500) before re-entering your home.
Can I use a smoke alarm to detect carbon monoxide?
No — smoke alarms and CO alarms are completely different devices and you need both. A smoke alarm detects particles from fire, whilst a CO alarm detects the gas itself, so you cannot substitute one for the other.
Why shouldn't I put a CO alarm directly above my boiler?
Placing an alarm too close to a gas appliance can cause false alarms from minor combustion variations and may prevent you from taking the device seriously when it actually detects a genuine problem. Mount it at head height in the same room or an adjacent room instead, keeping it at least 30cm away from the appliance.
How often should I replace my CO alarm?
CO alarms typically last 7–10 years depending on the manufacturer, and the lifespan date is printed on the unit itself. Check this date annually, replace batteries every year (even if they seem fine), and test the alarm monthly by pressing the test button to ensure it's still working.
Do I legally need CO alarms as a landlord?
Yes — from 1 April 2023, it's a legal requirement in England, Scotland, and Wales to fit at least one CO alarm in any room containing a fixed combustion appliance such as a boiler or gas fire. Failure to comply can result in significant fines, so check your properties now if you haven't already.
What should I do if my CO alarm keeps going off?
Turn off gas appliances, open windows to ventilate, evacuate everyone from the property, and call the Gas Safe Register's emergency line immediately — do not ignore it or assume it's a false alarm. Have a registered engineer inspect all gas appliances and your flue system before you switch anything back on.