Carbon monoxide poisoning: signs, causes and how a detector prevents it
Carbon monoxide has no smell, color or taste and kills people in their sleep. What produces it at home, the signs of poisoning, where to put a detector and what to do the moment the alarm sounds.
In short
- Carbon monoxide (CO) is invisible, odorless and non-irritating. The only reliable defense is a CO alarm.
- Symptoms look like flu: headache, dizziness, nausea, weakness, confusion. If several people at home feel it at once, think CO.
- Common sources: faulty or blocked stoves, boilers and chimneys, generators, grills and camping stoves used indoors.
- If the alarm sounds: everyone out into fresh air, then call the emergency number. Don't go back in until firefighters say it's safe.
Every winter, emergency services across Europe and North America deal with carbon monoxide poisonings, many of them affecting whole families at night because of a faulty stove or chimney. In the United States, the CDC estimates more than 400 deaths a year from accidental poisoning. Carbon monoxide is called the silent killer because you can’t sense it in any way, and its first symptoms make you want to lie down and sleep.
This guide is adapted from CDC and US public health guidance, which is in the public domain, and extended for European homes and heating systems.
What it is and where it comes from
Carbon monoxide is produced when any fuel burns incompletely: wood, coal, gas, gasoline, diesel, pellets. At home, the usual sources are:
- stoves and fireplaces with poor draft, a damper closed too early or a blocked chimney;
- gas boilers and water heaters that haven’t been serviced or whose flue is blocked;
- a gas oven or stove used to heat the house;
- generators, grills, burners and camping stoves used indoors, in a garage, on an enclosed porch or in a tent;
- a car left running in an attached garage, even with the door open.
Signs of poisoning
- headache, dizziness;
- nausea or vomiting;
- weakness, drowsiness;
- shortness of breath, chest pain;
- confusion, blurred vision;
- in severe cases, loss of consciousness.
It feels like flu or food poisoning. What gives it away: symptoms ease when you go outside, and they hit several people or pets in the same room at the same time. Children, older people, pregnant women and people with heart or lung disease are the most vulnerable.
If the alarm sounds or you have symptoms
- Get outside into fresh air at once, with everyone in the house and your pets. Don’t waste time looking for the source.
- Call the emergency number and say you suspect carbon monoxide poisoning.
- Don’t drive if you have symptoms.
- Don’t go back in until firefighters tell you it’s safe.
- Even if you feel better outside, see a doctor: effects can show up hours later.
If the alarm goes off and nobody has symptoms, open windows wide, turn off fuel-burning appliances and have a professional inspect them before using them again.
How to prevent it
- CO alarm near the bedrooms and in rooms with a stove, boiler or water heater
- Smoke alarm on every floor (a separate device unless it’s a combination unit)
- Chimney swept and inspected every autumn
- Boiler and water heater serviced every year by a qualified technician
- Never close a stove damper until the fire is completely out
- Never heat the house with a gas oven or stove
- Generator outdoors only, at least 6 meters (20 feet) from doors, windows and vents
- Never use a grill, burner or camping stove indoors, in a garage or in a tent
- Never leave a car running in a garage, even with the door open
- Test alarms monthly and replace them by the date printed on them
For winter power cuts, see also how to heat your home safely without power and our generator guide.
Older neighbors and relatives
Victims are often older people living alone in homes heated with old stoves. If you have parents or neighbors in that situation, a CO alarm is one of the most useful gifts you can give. Fit it yourself and show them what it sounds like.
Recommended equipment
What to look for when buying. Links go to partner shops; if you buy through them we may earn a small commission at no extra cost to you.Details.
Battery-powered carbon monoxide alarm
The cheapest way to prevent a fatal poisoning. Put one near the bedrooms.
- Certified to UL 2034 (US) or EN 50291 (Europe)
- Electrochemical sensor with a 7–10 year life
- Alarm of at least 85 dB, ideally with a digital readout
Combination smoke and carbon monoxide alarm
One unit for the hallway between bedrooms if you want to save space.
- Certified for both smoke and CO
- Long-life sealed battery
Frequently asked questions
Where should I put a carbon monoxide alarm?
At least one near the bedrooms, where you'll hear it at night, and one in each room with a stove, boiler, gas water heater or fireplace. Follow the manufacturer's instructions on height and distance from the appliance: usually not right next to the source, to avoid false alarms, and not in bathrooms or next to open windows.
Does a smoke alarm detect carbon monoxide?
No, unless it says explicitly that it's a combination (smoke and CO) alarm. They use different sensors. Ideally have both: a smoke alarm on every floor and a CO alarm near the bedrooms and fuel-burning appliances.
How long does a CO alarm last?
The sensor has a limited life, usually 7 to 10 years, and the replacement date is printed on the unit. Press the test button monthly and change the batteries when prompted or once a year, for example when the clocks change.
Can a stove that draws badly really kill me?
Yes. A stove with poor draft, a chimney blocked by soot or a bird's nest, or a damper closed too early sends combustion gases into the room. Most serious poisonings happen at night, during sleep, which is why an alarm and a yearly chimney sweep matter so much.
Sources and further reading
Preper is for general education and does not replace instructions from your local authorities or advice from a doctor. In an emergency, call your local emergency number.