Carbon monoxide at home: alarms, warning signs and what to do
3 min read · 8 steps · Updated 3 October 2026
Fit a carbon monoxide alarm in every room that has a fuel-burning appliance, such as a gas boiler, a gas fire or a wood stove, and have those appliances serviced once a year. If the alarm sounds or several people get headaches and feel sick at home, leave the building at once and call the emergency number.
Carbon monoxide (CO) is a gas you cannot see, smell or taste. It forms when gas, oil, coal, wood or charcoal burn without enough air, and it can kill in a short time. A smoke alarm does not detect it. An alarm made for CO costs little and is the only reliable warning.
If you rent, report faulty heating appliances, flues and cookers to your landlord at once. Repairs to gas appliances are a job for a registered engineer.
Step by step
Know where it comes from
Faulty or badly fitted boilers, cookers, heaters, gas fires and stoves, and blocked chimneys and flues. Also charcoal and gas barbecues, portable gas heaters, generators and car engines running in closed spaces.
Fit alarms
Put an alarm in every room with a fuel-burning appliance. If you can, add one in or near the bedroom, so it wakes you. Buy an alarm with a loud sounder that is certified to the European standard EN 50291. Colour-change stickers are not enough.
Place it correctly
Follow the instructions in the pack. As a rule, in a room with an appliance the alarm goes high on the wall or on the ceiling, one to three metres from the appliance and not directly above a cooker or next to a window. In a bedroom it goes at about the height of your head on the pillow.
Test it and note the date
Press the test button once a month. The sensor has a limited life, usually seven to ten years. The replacement date is printed on the alarm.
Watch the appliances
Warning signs are a lazy yellow or orange flame where it should be crisp and blue, black sooty marks or yellow-brown stains on or around the appliance, a pilot light that keeps going out, and more condensation on the windows than usual.
Know the symptoms
Headache, dizziness, tiredness, nausea, stomach pain, confusion and shortness of breath. It feels like flu or food poisoning without a fever. Typical clues: several people and pets are affected at once, and you feel better when you leave the home.
If the alarm sounds or you suspect CO
Stop using the appliances, open doors and windows on your way out, and leave the building at once. Call the emergency number, 112 in the EU, if anyone is unwell or has collapsed, and tell them you suspect carbon monoxide. Call the gas emergency service of your supplier from outside.
Do not go back in
Stay out until the fire service or an engineer has found the cause and it has been repaired. See a doctor the same day, even if you feel better, and say that you may have breathed in carbon monoxide.
Good to know
Have boilers, gas fires and stoves serviced once a year by a qualified engineer, and chimneys and flues swept and checked once a year. In Germany the chimney sweep (Schornsteinfeger) does the legally required check.
Never bring a barbecue, a charcoal grill or a camping stove indoors or into a tent or caravan to heat it. A barbecue gives off carbon monoxide for hours after it looks dead.
Never use a gas oven or hob to heat a room, and never block air vents.
The other alarm every home needs: smoke alarms: where to fit them and how to test them. Emergency numbers: emergency numbers in Germany.
In short: A CO alarm to EN 50291 in every room with a fuel-burning appliance, tested monthly. Yearly servicing. If it sounds or people feel ill: out into fresh air at once, call 112, do not go back in.
- London Fire Brigade: Carbon monoxide safety
Rules and prices change. Check the official source before you act.