What to Do If a Carbon Monoxide Alarm Goes Off

It is a winter evening and your family is watching TV when the CO alarm in the hallway starts blaring — loud, repeating beeps that are nothing like the quiet chirp you heard last month. Your first thought: "Is this real or is the battery dying again?" The safest answer is always the same: treat it as real first. CO is invisible, odorless, and can overwhelm people quickly — especially during sleep. Your goal is simple: get everyone into fresh air and get the home checked before you go back in. This page gives you a step-by-step emergency response, explains common scenarios, and links to troubleshooting guides for after the crisis.

This is general safety information — not medical advice. If a CO alarm sounds or you suspect exposure, move to fresh air and contact emergency services.

In 60 Seconds

Leave immediately with everyone (including pets). Do not search for the source indoors.
Call emergency services from outside — fire department or your building's emergency contact.
Do not re-enter until professionals confirm the building is safe.
If anyone has symptoms (headache, dizziness, nausea, confusion), seek medical help right away.
After clearance, fix the root cause — inspect fuel-burning appliances, vents, and flues before relying on "reset" alone.

First: Alarm vs Chirp — Know the Difference

People often say their "CO detector alarm is going off" when the unit is actually chirping for maintenance (battery, end-of-life, fault). The safest approach:

Loud, repeating alarm (or a display showing CO/PPM) = treat as a CO event. Evacuate.
Single chirp every 30–60 seconds (often with a flashing light) = usually battery, fault, or end-of-life.

If you are not sure which one you are hearing, assume the worst and evacuate. For chirp patterns and common fixes, see carbon monoxide detector beeping.

Step-by-Step Emergency Response

Step	Action	Key Detail
1	Get everyone to fresh air	Move outside. If cold, go to a neighbor's home or a car parked outside (not in a garage). Bring pets.
2	Call emergency services	Call from outside. Tell them a CO alarm activated. In apartments, also notify building management.
3	Do not "air it out and stay"	Opening windows can reduce CO temporarily, but CO can return when equipment restarts or wind shifts.
4	Treat symptoms as urgent	Multiple people feeling ill at once, or symptoms improving outdoors, are red flags. Seek medical help.
5	Return only after clearance	Wait for responders to confirm safety. Then schedule inspection of appliances, vents, and flues.

After Clearance: Fix the Cause

CO alarms are not the "problem" — they are the warning. Once responders say it is safe to return, the next job is prevention. Common next steps include:

Inspection of furnaces, boilers, water heaters, fireplaces, gas stoves, and any other fuel-burning equipment.
Checking vents, flues, chimneys, and exhaust paths for blockages and backdrafting.
Reviewing generator and vehicle practices — never run a generator indoors or near windows; never idle a car in an attached garage.
Replacing any alarm that is expired or malfunctioning. See how long CO detectors last.

For a broader prevention plan, see prevention of carbon monoxide poisoning.

Common Scenarios

"The alarm stopped after a few minutes — was it a false alarm?"

Not necessarily. CO levels can rise and fall with appliance cycles, wind, and ventilation changes. A short event is still a warning that something can produce dangerous CO under certain conditions. Treat it seriously and get an inspection.

"It is the middle of the night — do I really have to leave?"

Yes. Nighttime is high-risk because CO can affect judgment and wakefulness before you are fully aware. Evacuate first, then call for help. Plan ahead by keeping a phone, keys, shoes, and a warm layer easy to grab.

"I live in an apartment building"

Evacuate your unit, then notify building staff immediately. CO can originate in shared spaces — boiler rooms, garages, stacked vents — and affect neighboring units. Do not assume it is limited to your apartment. For apartment-specific guidance, see CO leak in an apartment.

Could It Be a False Alarm?

CO alarms can activate due to genuine CO, a failing sensor, low battery, or end-of-life behavior. Some environments (high humidity, dust, aerosols) can also cause issues on certain models. The safe sequence is always the same:

Evacuate and call for help if you cannot confidently rule out danger.
After clearance, troubleshoot the device — battery, reset, location, age.

If your unit is older, replacement is often the correct fix. Confirm proper placement using placement height guidance and the how many detectors checklist.

Frequently Asked Questions

Is it safe to open windows and stay inside when a CO alarm goes off?

No. Opening windows may reduce CO temporarily, but it does not confirm safety and can delay evacuation. CO can return quickly when equipment restarts or wind shifts. Leave and get professional confirmation before re-entry.

What if my CO alarm stops after a few minutes?

Do not assume it was harmless. CO levels can spike in short bursts during appliance cycles or ventilation changes. Arrange an inspection and review possible sources even if the alarm silences itself.

What if the CO alarm goes off in the middle of the night?

Evacuate immediately. CO exposure during sleep is a major risk because symptoms can impair judgment before you wake fully. Keep shoes, keys, a phone, and a warm layer easy to grab near your bed.

What should I do if a CO alarm goes off in an apartment building?

Evacuate your unit, call emergency services, and notify building management or security. CO can originate in shared spaces (boiler rooms, garages, stacked vents) and affect neighboring units.

Should I call the fire department for a CO alarm?

Yes — if the alarm is a loud repeating pattern (not a single chirp), if anyone has symptoms, or if you cannot identify the cause. Call from outside and do not re-enter until responders confirm it is safe.

Sources & References

Published: January 15, 2024