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Family in blankets outside a house on a winter evening, doors and windows wide open

The carbon monoxide alarm is going off

A shrill tone, but no smoke and no smell. That is exactly what makes carbon monoxide so dangerous – the alarm is your only nose.

First

  1. Take the alarm seriously – carbon monoxide cannot be smelled or seen.
  2. Open windows and doors wide if you can on your way out.
  3. Get all people and animals outside at once.
  4. Outside, call 112, even if nobody feels ill. Only go back in once the fire service or specialists allow it.

Call emergency services if

  • Always when the CO alarm sounds
  • Someone has a headache, dizziness, nausea or is confused
  • Someone is unresponsive
  • The alarm goes off again after airing

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What is happening

Carbon monoxide (CO) forms when fuels burn incompletely: in faulty or poorly ventilated heaters and boilers, in stoves and fireplaces with a blocked flue, and with grills, generators and engines in enclosed spaces. The gas is invisible, odourless and not irritating.

First symptoms resemble flu: headache, dizziness, nausea, weakness, confusion. Anyone asleep or who has been drinking can lose consciousness before noticing anything. It is typical that several people or pets in the same room have symptoms at the same time and feel better outside.

Health authorities such as the CDC advise: if the CO alarm goes off, get to fresh air at once and call the emergency number. In the EU that is 112. The fire service can measure, find the source and say when it is safe again.

This page describes the first steps. Medical treatment of poisoning belongs in the hands of the ambulance service.

Step by step

The carbon monoxide alarm is going off – Phase 1 of 4Alarm: windows open, everyone out. Take the alarm seriously – even if you smell nothing and feel fine. Open windows and doors wide as far as you can on your way out. Get all people and pets outside at once. Wake anyone asleep. If it is on your way: switch off the appliance, stove or engine. Do not go back for it.
Phase 1 of 4

Phase 1 of 4

Alarm: windows open, everyone out

Take the alarm seriously – even if you smell nothing and feel fine. Open windows and doors wide as far as you can on your way out. Get all people and pets outside at once. Wake anyone asleep. If it is on your way: switch off the appliance, stove or engine. Do not go back for it.

The animation shows the key actions of each phase schematically; the text below is what counts.

  1. Phase 1

    Alarm: windows open, everyone out

    • Take the alarm seriously – even if you smell nothing and feel fine.
    • Open windows and doors wide as far as you can on your way out.
    • Get all people and pets outside at once. Wake anyone asleep.
    • If it is on your way: switch off the appliance, stove or engine. Do not go back for it.

  2. Phase 2

    Outside: emergency call

    • Call 112: CO alarm, address, how many people are affected and what symptoms they have.
    • Stay in the fresh air, even if you feel better.
    • Count heads: is everyone out? Tell the fire service if anyone is still inside.
    • Do not go back into the building before the fire service has measured.

  3. Phase 3

    If someone has symptoms

    • On the emergency call, say who has which symptoms: headache, dizziness, nausea, confusion.
    • Let those affected sit quietly, keep them warm and do not leave them alone.
    • Put an unconscious person who is breathing normally in the recovery position, as taught in first-aid courses. Follow the dispatcher's instructions.
    • Do not put yourself in danger: anyone who starts feeling dizzy inside goes out at once.

  4. Phase 4

    Afterwards: have the source checked

    • Only use the suspect appliance again once a qualified person has checked it.
    • Have flues, chimneys and vents checked.
    • Test the CO alarm according to the manufacturer's instructions and do not remove it.
    • Never run generators, grills or outdoor heaters indoors, in garages or in basements.

★ Pro tips

What experienced people do differently: proven practice from mountain rescue, fire services, lifeguards and civil protection that beginners rarely know.

  1. CO alarms have an expiry date

    The sensor in a CO alarm lasts only a set number of years, usually five to ten depending on the model. Many units signal end of life with a distinct chirp that sounds different from the alarm. Write the replacement date clearly on the unit.

  2. Never warm up a car in the garage

    Even with the garage door open, carbon monoxide can build up and drift into the house, especially from an attached garage. Drive the car out first and let it run only in the open. The same goes for lawnmowers and other engines.

  3. Extractor hoods and fireplaces often clash

    A powerful extractor hood that vents outside can create negative pressure and pull fumes from a fireplace or gas boiler back into the room. That is why safety devices such as window switches exist. Ask your chimney sweep or heating engineer whether this has been checked in your home.

  4. A pulse oximeter misses CO poisoning

    A finger-clip pulse oximeter cannot tell carbon monoxide in the blood apart from oxygen. It may show normal readings even though someone is poisoned. So do not rely on it – get into fresh air and call the emergency number.

  5. Take a travel CO alarm

    Holiday flats, cabins, caravans and boats often have gas appliances but no CO alarm. A small battery-powered alarm fits in any bag. Put it near where you sleep.

What to watch out for

  • No smell, no warning

    CO has no smell. A CO alarm is the only reliable sign before symptoms appear.

  • “Flu” in the whole household

    If several people at home have headaches and nausea at the same time that improve outside, think of CO.

  • An open window is not enough

    A window left ajar does not make a generator or grill indoors safe.

  • Rescue in rooms full of CO

    Helpers can lose consciousness themselves. Only go in briefly if it can be done quickly – otherwise leave it to the fire service.

Common mistakes

  • Assuming the alarm is faulty and removing the battery.
  • Only airing out and staying inside.
  • Carrying on without calling because everyone feels fine.
  • Switching the appliance on again before it has been checked.
  • Running a grill or generator in a garage or basement.

Prepare in advance

  • CO alarms in rooms with fireplaces or gas appliances and near bedrooms, as the manufacturer advises.
  • Have heating, boiler, stove and chimney serviced regularly.
  • Never block or tape over vents.
  • In winter keep outside exhaust openings clear of snow if you can do so safely.
  • Show everyone in the household the difference between the smoke alarm and CO alarm sounds.

Special consideration

Pregnant women, children, older people
They are especially at risk from CO. Mention them on the emergency call even with mild symptoms.
Pets
Animals are poisoned by CO too. Take them out with you if it can be done quickly and have them checked by a vet if they seem unwell.

Sources

  • Carbon Monoxide Poisoning – Prevention guidance · Centers for Disease Control and Prevention
  • WHO guidelines for indoor air quality: selected pollutants (carbon monoxide chapter) · World Health Organization, Regional Office for Europe, 2010
  • 112 – the European emergency number · European Commission

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All rules of this situation (4)

  1. [not active] If How is everyone? = Headache, dizziness, nausea, tiredness

    Symptoms such as headache, dizziness or nausea can be signs of poisoning. Stay in the fresh air, call 112 and describe the symptoms.

  2. [not active] If How is everyone? = Someone is confused or unresponsive

    Call 112 at once. Do not put yourself at risk: throw windows open and only bring the person out if you can do it quickly. Outside, keep helping as the dispatcher instructs.

  3. [not active] If Possible source = Generator, grill or engine nearby

    Generators, grills and engines never belong indoors, in garages or basements – not even with a window open.

  4. [not active] If Possible source = Heating, boiler, gas appliance or Fireplace, stove

    Do not use the appliance again until a qualified person has checked it. Do not repair it yourself.