Treat a full alarm as a real emergency
Carbon monoxide is colorless and odorless, so people cannot use their senses to judge whether a home is safe. A sounding carbon monoxide alarm is a warning of a potentially life-threatening gas. Do not wait to see whether anyone develops symptoms, do not search room by room for the source, and do not assume the alarm is false because a fuel-burning appliance appears to be working.
CPSC and fire-safety guidance say to move everyone, including pets, to fresh air and call emergency services from outside. If anyone has headache, dizziness, weakness, nausea, vomiting, chest pain, confusion, shortness of breath, or loss of coordination, tell responders about the alarm and seek medical help. Do not reenter to collect belongings or silence the device.
Leave without creating another hazard
If it is immediately accessible and safe, open a door on the way out, but do not delay evacuation to ventilate, turn off appliances, find a pet, or locate the alarm. Do not turn lights or switches on and off, start a vehicle in an attached garage, or use a generator, grill, stove, fireplace, or portable fuel-burning heater while deciding what happened.
Tell responders which alarms sounded, where people were located, whether a generator or vehicle was running, and whether the home uses gas, oil, propane, wood, or other fuel-burning equipment. If you can see smoke or fire, follow fire-escape instructions and stay outside. A CO alarm can indicate a venting, combustion, or equipment problem even when there is no visible smoke.
Do not confuse an alarm with a low-battery chirp
A full alarm is usually a repeating pattern described in the manufacturer's instructions. A single periodic chirp can indicate a low battery, end of service life, or fault, but occupants should not guess when the sound, display, or location is unclear. If the device is sounding continuously or anyone feels ill, treat it as a CO emergency and leave.
After responders establish that no CO hazard is present, replace batteries and the alarm according to the instructions. Do not remove a battery and leave the alarm disabled. Record the device model, date, room, sound pattern, displayed reading if any, and whether other alarms were interconnected. Never assume a silent alarm means the air is safe if the device is expired, missing, or not powered.
- Full alarm or repeating warning
- Single chirp or end-of-life signal
- Displayed concentration or error code
- Alarm location and connected appliances
- Symptoms or illness
- Recent outage, storm, generator, or heating change
Wait for clearance before returning
Do not reenter until fire, emergency, utility, or other qualified responders say it is safe. Opening windows may lower a reading temporarily without fixing a blocked vent, backdraft, cracked heat exchanger, failed appliance, vehicle exhaust, or generator placement. Do not reset a furnace, water heater, fireplace, or appliance and resume use without an inspection when CO was detected.
If the source is not obvious, ask responders what equipment must remain off and who is qualified to test it. The home may need a licensed HVAC or appliance professional, chimney or vent inspection, utility response, or a certified combustion and CO evaluation. Keep written clearance and repair information with the home's safety records.
Investigate fuel-burning equipment and pathways
Possible sources include furnaces, boilers, fireplaces, gas ranges, water heaters, portable generators, vehicles, charcoal grills, and small engines. Blocked chimneys, snow-covered vents, disconnected flues, poor combustion air, damaged heat exchangers, and exhaust entering from a garage can all matter. A professional should inspect the appliance, venting, chimney, combustion air, and surrounding conditions.
Do not use a gas range or oven to heat the home. Never use a portable generator or charcoal grill indoors or in a garage, even with the door open. Keep generators outdoors at least 20 feet from the home with exhaust directed away from doors, windows, and vents, following CPSC instructions and the generator manual.
- Fuel-burning furnace or boiler
- Gas water heater
- Fireplace, wood stove, or chimney
- Gas range or oven
- Portable generator or engine
- Attached garage and vehicle exhaust
- Blocked outside vent or flue
Rebuild reliable alarm coverage
Install CO alarms on every level and outside each separate sleeping area, using battery backup or battery operation as appropriate. Interconnected alarms can warn occupants throughout the home when one device detects CO. Follow the manufacturer's placement rules and avoid locations where cooking vapors or airflow can create nuisance alarms. Do not place a CO alarm in an attic or basement unless it contains a sleeping area, and do not use it as a substitute for a smoke alarm.
Test alarms monthly, replace batteries as directed, and replace the alarm at the manufacturer's end-of-life interval. CDC advises replacing detectors according to the instructions or every five years. Keep a simple list of device locations, installation dates, battery changes, tests, and replacement dates. A test button verifies the alarm's function, not the absence of CO at every moment.
Prevent a repeat event
Have fuel-burning heating systems, chimneys, and vents inspected and serviced annually by a trained professional. Keep outside vents clear of snow, leaves, nests, and stored items. Never run a vehicle in an attached garage, even with the door open. Keep generators, grills, and engines outside at the distances specified by CPSC and the equipment instructions.
If the home has a new appliance, remodel, sealed-up chimney, new windows, or an added exhaust fan, ask whether combustion air and venting need review. Do not seal, extend, or alter a flue yourself. When a CO event occurs, retain the alarm record and professional report so a future technician can see what was tested and what was changed.
Frequently asked questions
What should I do first when a CO alarm sounds? Get everyone and pets outside to fresh air, then call emergency services from outside. Should I find the source? No. Evacuate and let responders and qualified professionals investigate. Can I go back in after opening windows? Not until responders say it is safe. What symptoms matter? Headache, dizziness, weakness, nausea, vomiting, chest pain, confusion, shortness of breath, and loss of coordination can occur, but do not wait for symptoms before leaving. Is a chirp the same as an alarm? It may indicate low battery or end of life, but follow the manufacturer instructions and treat an uncertain or sustained alarm as real. Where should CO alarms go? On every level and outside sleeping areas, following product instructions. Can a smoke alarm detect CO? Not unless it is specifically a combination smoke and CO alarm. How often should I test it? Monthly, and replace batteries and the device on the manufacturer's schedule. Can a generator run in a garage with the door open? Never. Keep it outdoors and away from doors, windows, and vents as directed.