What should I do when a carbon monoxide alarm sounds?
Treat a sounding CO alarm as an emergency because carbon monoxide cannot be seen, smelled, or tasted.
Urgency: emergency
What this means
Leave immediately for fresh air and call emergency services from outside.
Safe checks
- Take everyone and pets outside
- do not search for the source
- call 911 or the fire department
- return only after professionals say it is safe.
Stop and get help if
- Do not silence the alarm and remain inside, ventilate instead of leaving, or re-enter to retrieve belongings.
Which professional to call
Contact the matched licensed or qualified trade if safe checks do not resolve the issue.
Find the relevant tradeSource and method
This answer combines HomeSOS's structured triage with safety boundaries supported by a public source. It does not replace inspection.
Health Canada: Home safety and indoor air guidanceReviewed August 12, 2026