If your CO alarm is going off, get everyone out of the house immediately and call 911 from outside. Do not waste time opening windows or searching for the source. Carbon monoxide is colorless and odorless, so you cannot tell how dangerous the situation is without professional equipment. Most people who search for a “CO2 alarm” are actually dealing with a carbon monoxide (CO) detector, which is the standard alarm installed in homes. That’s what this article covers.
Step by Step: What to Do Right Now
The U.S. Consumer Product Safety Commission is clear on the protocol: everyone in the home, including pets, should go outside or to a neighbor’s house immediately. Do not take time to ventilate the home first. Do not go looking for the source of the leak. Once outside, call 911 or your local fire department.
If someone is unconscious or physically unable to leave, open windows and doors in the room they’re in while you help them out. Otherwise, ventilation can wait.
Do not re-enter the home until emergency responders have inspected it and told you it’s safe. Even if the alarm stops sounding, that doesn’t mean the CO has cleared or that the source has stopped producing it.
In extreme weather where going outside or to a neighbor isn’t realistic, stay in one room with a window or door open to the outside. Close interior doors to the rest of the house. Turn on an exhaust fan if the room has one. Make sure no fuel-burning appliances are running in that room and no vehicles are idling in the garage.
Symptoms to Watch For
Carbon monoxide poisoning starts subtly. At lower exposure levels, you’ll get a mild headache that’s easy to dismiss. As exposure increases, symptoms progress to dizziness, nausea, confusion, and impaired coordination. At high levels, people become too confused and uncoordinated to get themselves out of the house, which is what makes CO so dangerous.
If anyone in your household has a headache, feels dizzy, or is nauseous when the alarm sounds, tell the 911 dispatcher. Emergency responders will prioritize differently if people are symptomatic. Even mild symptoms warrant medical evaluation, because CO displaces oxygen in your blood and the effects can linger or worsen after you’ve left the exposure.
Why the Alarm Might Not Be a False Alarm
Home CO alarms follow a standard that prevents them from going off at trace levels. At 70 parts per million, an alarm won’t sound until at least 60 minutes of sustained exposure. At 150 ppm, it must sound within 10 minutes. At 400 ppm, which is immediately dangerous, alarms are required to go off within 4 to 15 minutes. So if your alarm is sounding, the CO concentration has been elevated long enough to meet one of these thresholds. Take it seriously.
That said, alarms near the end of their lifespan can produce beeping that sounds like an alert. CO alarms last about seven years, and when they expire, they beep every 30 seconds or display “ERR” or “END.” This is distinct from a continuous alarm pattern. Check your alarm’s display if it has one. If you see an error code and the beeping is a slow, periodic chirp rather than a sustained alarm, you likely need a replacement, not an evacuation. When in doubt, evacuate anyway.
Common Sources of Carbon Monoxide in Homes
Heating equipment is the leading cause of residential CO problems. Furnaces, water heaters, gas fireplaces, and wood stoves all produce carbon monoxide as a byproduct of combustion. When they’re working correctly, exhaust vents carry the gas outside. When something goes wrong (a cracked heat exchanger, a blocked chimney, a disconnected vent pipe) the CO enters your living space instead.
Other common sources include:
- Blocked vents: Furnace and dryer vents clogged by debris, ice, or bird nests
- Vehicles in garages: Even with the garage door open, fumes migrate into the home quickly
- Portable generators: A frequent cause of fatal CO poisoning, especially during power outages
- Gas ovens used for heating: Ovens are not designed for continuous operation and lack proper venting for that purpose
- Charcoal or propane grills used indoors: These should never be operated inside or in enclosed spaces
- Snow-blocked tailpipes: A buried tailpipe pushes exhaust back into the vehicle’s cabin
- Gas-powered yard tools: Running a leaf blower or snow blower near an open door or window can push CO inside
Who to Call After the Emergency
Once the fire department has cleared your home and identified (or ruled out) an immediate danger, you’ll need to find and fix the underlying source. The fire department can tell you if CO levels were elevated and may be able to narrow down the general area, but they typically don’t do appliance repairs.
Your next call depends on what you suspect. For furnaces, water heaters, and other gas appliances, contact an HVAC technician or your gas utility company. Many gas companies will send someone to inspect for free. For fireplaces and wood stoves, a chimney sweep can check for blockages. If you have no idea where the CO came from, an HVAC professional with CO detection equipment can systematically test each appliance.
Don’t use any fuel-burning appliance that’s under suspicion until it’s been inspected. If your furnace was the likely culprit and it’s winter, use electric space heaters in the meantime.
Preventing Future Alarms
Have all fuel-burning appliances inspected annually, ideally before heating season starts. This includes your furnace, water heater, fireplace, and any gas dryer. A technician will check vent connections, heat exchangers, and combustion efficiency, all of which deteriorate over time.
Check vent pipes, flues, and chimneys yourself periodically for visible damage, disconnections, or blockages. Birds and small animals frequently nest in exhaust vents during warmer months, creating blockages that only become a problem once you fire up the furnace in fall.
Replace your CO alarms before they expire. The seven-year lifespan is a hard limit on the sensor’s reliability, not a suggestion. Write the installation date on the alarm in marker so you don’t have to guess later. Test alarms monthly using the test button, and replace batteries annually if your unit uses them. Some newer models have sealed 10-year batteries and a matching sensor lifespan, which eliminates the battery replacement step entirely.
Install CO alarms on every level of your home and near sleeping areas. CO can accumulate in one part of the house before reaching another, so a single alarm in the basement won’t necessarily protect bedrooms on the second floor.