CANADA — If your carbon monoxide (CO) alarm sounds a full alarm, leave the building immediately with everyone who can safely evacuate. Move into fresh air. From outside call 911, your local fire department or emergency services. Do not look for the leak, silence the alarm and stay inside, or re-enter until qualified responders say it is safe.
Do these 12 things immediately — carbon monoxide alarm checklist
- 1. Treat the CO alarm as real. Carbon monoxide cannot be seen, smelled or tasted. Symptoms may be absent at first.
- 2. Leave the building immediately. Tell all occupants to go to fresh outdoor air without stopping to investigate the source.
- 3. Help children and people who need assistance. Move infants, older adults and people with mobility needs by safe exits.
- 4. Do not go searching for a malfunctioning furnace, stove or generator. Never delay evacuation to find or photograph the suspected source.
- 5. From outside, call 911 or local emergency services. Say “carbon monoxide alarm” and provide the precise street address, unit number and whether anyone has symptoms.
- 6. Watch for illness. Headache, nausea, dizziness, weakness, confusion, chest pain or unusual sleepiness may signal exposure.
- 7. Get urgent medical evaluation for possible poisoning. Tell responders who has symptoms and whether anyone was asleep or unconscious.
- 8. If someone collapses, do not re-enter unsafely to rescue them. Tell the dispatcher their last known location and follow emergency instructions.
- 9. Keep everyone away from the building. Do not wait in an attached garage, porch or place where exhaust or gas may accumulate.
- 10. Do not restart or test fuel-burning equipment. Leave investigation, ventilation and repairs to emergency responders and qualified technicians.
- 11. Report generator, barbecue or vehicle use. Tell responders if any fuel-burning item may have been operating indoors, in a shed or garage.
- 12. Return only after the hazard has been identified and corrected. Follow emergency services and professional clearance; then maintain or replace the alarm as required.
If your CO alarm is sounding now, go outside before reading further. This guide explains why those first steps matter and what to do afterward.
Carbon monoxide is a poisonous gas created when fuel burns. It may accumulate around faulty heating equipment, blocked vents, portable generators, barbecue grills or vehicles in enclosed garages. People may think an alarm is a nuisance or a detector fault, particularly if the home looks normal and nobody feels ill. That assumption can be dangerous.
Health Canada instructs occupants to leave the home immediately, move to fresh air, avoid trying to locate the source, call emergency services from outside, and return only after professional correction. The Canadian federal guidance applies even when the source is unclear, because CO cannot be detected reliably by human senses.
Fast navigation — find the answer
Why CO is dangerous · Leaving safely · Symptoms · Full alarm or battery chirp? · Common sources · Winter and outages · After professionals attend · FAQs · Official sources
Why carbon monoxide is an emergency even without smoke
CO has no colour, smell or taste. It can move through occupied rooms and interfere with oxygen transport in the body. Headache, dizziness and nausea may look like ordinary influenza or fatigue. Several people in one household developing similar symptoms at the same time is especially concerning and should be reported to responders.
Unlike a smoke alarm, a carbon monoxide alarm may signal a dangerous gas when there is no visible fire, smoke or unusual smell. Do not assume that because nobody is coughing or because a pet is active, the air is safe. Early symptoms may be mild and worsen with continued exposure.
Exposure severity depends on concentration and duration as well as individual vulnerability. Health Canada notes that infants, pregnant people, older adults, people with heart or lung conditions, and people with anemia may be at increased risk. The proper response is to leave and let trained personnel evaluate both the building and people.
How to leave safely when the alarm begins
Tell household members clearly: “The carbon monoxide alarm is sounding. We need to go outside now.” Use the nearest usable safe exit. Do not take time to find the source in a basement, test a boiler, switch a generator off deep inside a garage, or stand in the kitchen studying the alarm manual.
Gather occupants at a location safely away from the building and any nearby exhaust source. An attached garage is not a safe meeting point. In a multi-unit building, use appropriate exits and alert the emergency operator to others who may be exposed. If a person cannot evacuate safely, give dispatch their exact room or floor and do not create a second casualty by re-entering.
Once outdoors, call 911 or your local fire department/emergency services according to your area. Tell them the alarm has sounded, whether symptoms are present, the address and whether any vulnerable or trapped people remain. Avoid cancelling the call because the noise stops or an alarm resets.
Do not re-enter to rescue possessions
A phone, medication bag, pet carrier or wallet may be essential later, but returning to an uncleared home can expose you to carbon monoxide. Report anyone trapped and the location to firefighters; follow their instructions on any urgent medical need or rescue. Arrange replacement medication and temporary accommodation through appropriate services rather than entering unprotected.
Symptoms of carbon monoxide exposure
Health Canada lists headache, tiredness, shortness of breath and flu-like symptoms with lower exposure; more severe exposure may cause dizziness, chest pain, difficulty thinking, visual problems, seizures, unconsciousness and death. Symptoms alone do not tell you whether the building is safe, and a person may have been exposed while sleeping without recognising early warning signs.
Emergency clinicians may provide oxygen and tests to assess exposure and injury. Do not attempt to diagnose or exclude poisoning at home. Ordinary fingertip pulse oximeters can give misleading oxygen readings in carbon monoxide poisoning, according to British Columbia Emergency Health Services’ clinical guidance.
Tell clinicians if a person is pregnant, has a heart condition, lost consciousness or was exposed for an uncertain period. If someone is unconscious and not breathing normally, follow the 911 dispatcher’s directions for CPR, but never enter a hazardous area to perform rescue without trained protection.
Is it a true CO alarm or a low-battery chirp?
Many detectors use different sounds for a full CO alarm, low battery, fault and end-of-life condition. A periodic chirp is not necessarily the same as a repeating emergency alarm pattern. Models differ, so the manufacturer’s manual or markings on the alarm are the reliable way to understand its signals in advance.
Toronto Fire Services describes checking the battery or end-of-life alert when there are no symptoms and a device gives a non-emergency warning. However, Health Canada’s national advice is clear about a CO alarm: leave immediately and seek help from outside. If you cannot positively distinguish a chirp from a full alarm, treat the situation as a potential emergency rather than experimenting inside.
Do not remove the batteries from a sounding CO alarm simply to stop the noise. If a device genuinely has an end-of-life or power fault, fix or replace it after the environment is known to be safe. Follow your provincial or municipal installation requirements.
Where carbon monoxide can come from
- Furnaces and boilers: incomplete combustion or blocked ventilation can create indoor exposure.
- Gas and wood fireplaces: poor maintenance, blocked flues or improper operation can lead to risk.
- Vehicles: running a car or other engine in an attached garage can send CO into the home, even with a door open.
- Portable generators: fuel-burning units used in garages, sheds or near doors and windows can poison indoor air.
- Charcoal grills and camping stoves: these are not safe indoor heating solutions.
- Fuel-powered tools: lawnmowers, snowblowers and similar equipment can produce exhaust in enclosed areas.
Carbon monoxide risk is not limited to natural-gas appliances. Propane, gasoline, heating oil, wood and charcoal can all produce CO when burned. A building may also be affected by exhaust from an adjacent garage, connected space or another source. Do not assume one appliance is responsible without an authorised investigation.
During Canadian winter storms and power outages
Cold weather and an electricity outage may tempt residents to use a barbecue or camping stove indoors, or to put a generator in a garage so it stays dry. Health Canada warns against both. A portable fuel-burning generator must be operated outdoors, at least six metres (20 feet) from homes and other buildings, with exhaust directed away from windows and doors; follow any stricter equipment or local rules.
Never heat a house with a gas oven or cooktop, and never run a vehicle inside an attached garage, even with the garage door open. If the home cannot be kept warm safely, seek a municipal warming centre, an approved heated shelter or another safe location rather than improvising fuel-burning indoor heat.
Snow and ice can block exterior vents and chimneys. Such hazards need safe inspection and maintenance; do not climb onto an icy roof or remain in a suspect building to clear a vent while an alarm is active. Tell firefighters if recent snow accumulation or generator use might be relevant.
Practical situations — what to do in each one
The alarm sounds at 3 a.m. while everyone is asleep
Wake household members and evacuate directly to fresh outdoor air. Call 911 from outside and provide the address and names of people who were asleep. Do not spend time proving who has symptoms, making coffee or checking whether the furnace is on.
Nobody feels ill but the detector makes a loud repeating alarm
Leave anyway. A full CO alarm is not safely dismissed by the absence of symptoms. Call the appropriate emergency service from outside and wait for professional advice before re-entering.
You are in a condominium or apartment building
Move to safety and tell responders your unit, floor and any potentially exposed neighbours or shared utility spaces. Do not assume a detector sounding in one apartment cannot concern adjacent units. Follow the building’s emergency plan and directions from firefighters.
A neighbour’s generator is running near your window
If you suspect exhaust may be entering your home or a CO alarm sounds, get into fresh air and contact emergency services. Do not enter another person’s shed or attempt to handle their operating generator. Provide responders the location of the suspected source.
A family member becomes dizzy after a garage was used
Move everyone to fresh air and contact emergency medical services promptly. Describe whether a car or engine was operated, the approximate time, and symptoms. Do not rely on a personal fingertip oxygen monitor to rule out CO exposure.
Children, pregnancy and pets
A baby or young child cannot reliably tell an adult about headache or dizziness. Older adults or people with cognitive limitations may have trouble reporting symptoms. If the alarm operates, evacuate them promptly and tell responders who might need help or clinical assessment.
Pregnant people should inform medical responders about their pregnancy even if they feel relatively well. The consequences of exposure may not be clear based only on how the person feels. Medical professionals determine appropriate testing and treatment.
Bring pets only when you can do so without delaying or endangering the evacuation. Report animals left inside to the fire service and do not re-enter to find them. Veterinary assessment may be appropriate for a pet that appears unwell after possible exposure.
What happens after firefighters or technicians attend
Emergency responders may measure CO levels, investigate ventilation and identify unsafe fuel-burning equipment. A qualified heating professional may need to repair a furnace, boiler, flue or other installation. A problem can appear intermittent, so do not assume that fresh air or the detector falling silent proves repairs are unnecessary.
Return only when the hazard has been assessed and corrected and the appropriate authority says it is safe. If heating is unavailable during winter, arrange somewhere warm to stay without using unsafe substitute heaters. Keep records of professional reports and any required maintenance for the property owner, insurer or landlord.
If you rent, notify your landlord or building manager after reporting the emergency. Do not wait for a routine maintenance appointment before seeking urgent help when the CO alarm sounds. The landlord’s repair process and emergency services’ response have different purposes.
Preventing a future CO incident
- Install certified CO alarms according to local law and manufacturer placement instructions, particularly near sleeping areas.
- Test alarms and replace batteries or devices as the instructions require.
- Teach household members the difference between a full emergency alarm and a battery or end-of-life signal.
- Have fuel-burning appliances, chimneys and vents inspected and maintained by qualified professionals.
- Keep exterior exhaust vents clear of snow, debris and blockages when safe.
- Never use generators, barbecues or camping stoves inside homes, sheds or garages.
- Place generators outside at least six metres from buildings, with exhaust away from windows and doors.
- Never idle a car or other engine inside an attached garage.
- Set an outside family meeting place and plan assistance for anyone with limited mobility.
- Save the local emergency number and arrange a safe winter warming alternative.
Common mistakes to avoid
- Looking for the CO source before leaving. Health Canada specifically says not to do this.
- Assuming that no odour means no gas. CO is odourless.
- Disabling or removing a sounding alarm. This hides warning without making the air safe.
- Running a generator in a garage, shed or covered indoor space.
- Using a gas oven or barbecue as a room heater.
- Returning after the alarm falls silent without professional clearance.
- Using an ordinary pulse oximeter reading to dismiss possible poisoning.
- Ignoring children or people who were asleep during an exposure.
Frequently asked questions
What should I do if a CO alarm sounds in Canada?
Leave immediately, move to fresh air and call 911 or local emergency services from outside. Do not find the source yourself or return until the hazard is corrected by a professional.
Can I stay if there is no smell?
No. Carbon monoxide has no smell, taste or colour, so you cannot judge its presence by your senses.
What if the alarm stops by itself?
Do not assume the building is safe. Follow the instructions from emergency services and qualified professionals before returning.
Is one short chirp the same as the full alarm?
Many alarms use separate signals for low battery and CO detection, but patterns vary. Learn your model’s signals in advance; if uncertain whether it is a full CO alarm, evacuate and ask for help.
How far should a generator be from the house?
Health Canada recommends at least six metres (20 feet) from any home or building, outdoors, with exhaust directed away from openings. Follow stricter local or manufacturer requirements.
Can a finger oxygen monitor show that I am safe?
Not reliably. Standard pulse oximetry may be misleading in carbon monoxide poisoning; medical responders determine the required assessment.
What if an older relative cannot walk downstairs?
Call emergency services from a safe location, explain the floor, location and mobility needs, and follow rescue instructions rather than risking an unprotected re-entry.
The sequence to remember
Alarm → fresh air → call emergency services → medical assessment when needed → professional correction → authorised re-entry. Nothing in a normal-looking room proves carbon monoxide is absent.
For related preparation during a winter outage, see What to Do When the Power Goes Out in a Canadian Winter.
Verified official sources and further reading
Guidance checked on 4 November 2026. Use current local emergency instructions in a real incident. This independent guide is general public information, not personalised medical or fire-safety advice.