Quick answer
Fit an audible carbon monoxide alarm suitable for its intended location, follow its installation instructions and maintain fuel-burning appliances properly. If an alarm sounds or poisoning is suspected, get outside promptly, seek appropriate emergency or medical help and do not return until advised it is safe.
An alarm is one layer of protection
Carbon monoxide, usually shortened to CO, is a poisonous gas produced by incomplete combustion. Gas, oil, wood, coal, petrol and other fuels can be involved. You cannot reliably detect it by sight or smell. A working audible alarm provides an important warning, but it does not prevent a fault, make an unsafe appliance acceptable or replace competent installation, servicing and ventilation. Think of prevention, detection and a clear response as three separate tasks.
This matters throughout the year, not just during electricity interruptions. A faulty boiler, blocked flue or wrongly used portable appliance can cause a problem during an otherwise ordinary day. During a power cut, avoid changing familiar routines in ways that introduce combustion indoors. Prepare food that does not need heating and use battery lighting where possible. You do not need a dramatic risk statistic to justify a practical safety check.
Know when to get outside and seek help
If a CO alarm sounds, get everyone outside promptly, including children and anyone who needs help moving. Do not delay leaving to investigate the appliance, retrieve possessions or repeatedly reset the alarm. If you can switch off a suspected appliance safely on the way out, without delaying evacuation, do so. Call for help from outside and do not return until the appropriate professionals advise that it is safe.
Call 999 for a medical emergency, including severe breathing difficulty, collapse, loss of consciousness or serious confusion following suspected exposure. The NHS advises seeking medical advice promptly when poisoning is suspected, with NHS 111 for possible symptoms where it is not an immediate emergency. Explain that carbon monoxide may be involved. A gas-emergency call is not a substitute for medical assessment, and feeling better outdoors does not prove that no harm has occurred.
Recognise symptoms without waiting for a perfect pattern
The NHS lists headache, dizziness, nausea or vomiting, weakness, tiredness, confusion, chest or muscle pain and shortness of breath among possible symptoms. They can resemble common illnesses and may come and go. Symptoms worsening inside a building and improving after leaving are a warning sign, not a reason to return and test the theory. More than one person feeling unwell in the same space is another reason to take the situation seriously.
Do not wait for every household member to develop symptoms or for a display to show a particular number. An alarm is not a medical diagnostic instrument, and a silent alarm does not rule out exposure. Tell the clinician where you were, what appliances were operating and roughly when you left. Never re-enter a suspect room to rescue a pet or find the source if doing so puts you at risk; tell the emergency services who or what remains inside.
Choose an audible alarm for the intended setting
Look for a reputable supplier, clear manufacturer details, installation instructions and conformity with the relevant BS EN 50291 standard. HSENI recommends audible alarms and does not recommend relying on colour-changing “black spot” cards as a warning system. A display can be useful, but the ability to give an effective audible warning is central. Read the specification carefully rather than choosing only by price, appearance or a marketplace star rating.
Check whether the device is intended for a home, caravan, motorhome or boat; not every domestic product is suitable for every environment. Consider a sealed battery model or a mains-powered model with suitable backup, depending on the installation. The important point during a power cut is that the warning function continues. For a person who may not hear an alarm, ask about compatible visual or vibrating warning equipment rather than assuming a louder standard unit will solve the problem.
Follow the installation instructions, not a one-line rule
There is no useful universal instruction to put just one CO alarm on each floor and consider the job finished. Coverage depends on fuel-burning appliances, sleeping arrangements, room layout and the selected alarm’s instructions. Fire-service guidance commonly discusses positioning in relation to the appliance and occupied areas. Read the actual installation leaflet before mounting anything, and ask the manufacturer or a competent installer if the room presents an unusual layout.
Avoid hiding an alarm behind furniture, inside a cupboard or where curtains can obstruct it. Do not put it beside a vent or window simply because the location is convenient. Humidity, temperature and direct cooking fumes can affect suitability, so check the permitted conditions. Keep the warning audible from sleeping areas, with additional compatible provision where needed. A portable alarm on a shelf is only appropriate if the instructions permit that arrangement and the location meets them.
Test, record and replace the whole unit when due
Use the test button at the interval stated by the manufacturer and follow any cleaning instructions. Never test an alarm with a flame, vehicle exhaust or another improvised source of CO. Record the installation date and replacement date somewhere visible, and keep the instructions where everyone can find them. Test-button operation checks specified functions; it does not certify that every appliance or flue in the property is safe.
Learn the difference between the emergency warning, a low-battery signal and an end-of-life or fault signal by reading the manual before a problem occurs. If you are unsure whether a sounding alarm is warning of CO, prioritise getting outside rather than guessing. Replace batteries only where the design allows it, and replace the entire alarm at its specified end of life. A fresh battery does not renew an expired sensor, and there is no single lifespan applicable to every model.
Keep portable combustion equipment outside
Never use a barbecue or camping stove inside a home, tent, caravan or other enclosed accommodation. A partly open window does not make an outdoor-only appliance safe indoors. Charcoal can continue producing CO while cooling, so do not bring a used barbecue inside for warmth. Do not use an oven or cooker as a room heater. Keep required ventilation openings clear and use installed appliances only for their intended purpose.
Portable generators also produce dangerous exhaust. Never run one inside a home, garage or other enclosed space, including a garage with its door open. Locate it outdoors according to the manufacturer’s safety instructions and appropriate guidance, with exhaust kept away from doors, windows, vents and neighbouring properties. Do not present a single distance as a guarantee: wind, building layout and openings matter. An alarm does not turn an unsafe generator position into an acceptable one.
Know the limits of rental rules
Housing requirements differ across England, Scotland, Wales and Northern Ireland, and can also depend on the property and tenancy. Do not apply one country’s rule to the whole UK. In England, the 2022 amendments require relevant landlords to provide a CO alarm in a room used as living accommodation containing a fixed combustion appliance, excluding gas cookers. That is wider than the older description covering only solid-fuel appliances.
The England guidance also addresses repairing or replacing alarms once reported and found faulty. Tenants should report defects promptly in writing and keep a record; nobody should remain in suspected exposure while waiting for a maintenance appointment. Ask the landlord or housing provider which current requirements apply locally, and contact the local authority if necessary. Legal minimum coverage and sensible additional protection are not always identical, especially where a person has particular hearing or support needs.
Make the household response simple
Write a short instruction near the household plan: leave, account for everyone, call for appropriate help and stay out until advised. In Great Britain, the National Gas Emergency Service number is 0800 111 999 for suspected gas-related danger; Northern Ireland and other countries have different arrangements, so record the correct local contact. For oil or solid-fuel concerns, use the relevant emergency or competent professional service rather than assuming the gas number covers every situation.
Arrange competent appliance maintenance: gas work should be carried out by a suitably qualified Gas Safe registered engineer, and other fuel systems need appropriately competent specialists. Keep service records and check that vents and flues are not blocked. Combine this with working smoke alarms, battery lighting and a no-cook food option. A calm, familiar routine is more valuable than reassurance based on an alarm that nobody has tested or knows how to respond to.
Related practical guides
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Sources
Sources checked for this editorial revision; accessed 9 November 2026. Check current official guidance before acting.
- NHS: carbon monoxide poisoning — accessed 9 November 2026.
- Devon and Somerset Fire and Rescue Service: carbon monoxide — accessed 9 November 2026.
- HSENI: carbon monoxide alarms — accessed 9 November 2026.
- GOV.UK: alarm regulations guidance for England (29 July 2022) — accessed 9 November 2026.
- GOV.UK Be Ready: household preparedness — accessed 9 November 2026.