Short answer
If the CO alarm sounds its alarm pattern, get everyone outside and call 911. Don't go back in until responders say it's safe. Then have a licensed HVAC tech test every gas appliance before using them again. A single chirp every 30–60 seconds usually means a low battery or end of life.
Alarm vs. chirp
An alarm is a loud repeating pattern, usually four beeps. A chirp is a single short sound at intervals, which signals battery or end-of-life.
Common sources
Furnaces, water heaters, gas ranges, fireplaces and running vehicles in attached garages.
- Blocked or disconnected flue
- Cracked heat exchanger
- Backdrafting water heater
- Car warming up in the garage
What the tech does
Measures CO at each appliance and in the living space, inspects venting and the heat exchanger, and shuts off unsafe equipment.
Symptoms of carbon monoxide exposure
CO is colorless and odorless. Early symptoms resemble the flu: headache, dizziness, nausea, weakness and confusion. Symptoms that improve when you leave the house and return when you come back are a warning sign. Get fresh air and medical help.
After the fire department clears the home
Responders can confirm whether CO is present, but they don't repair appliances. Before using the furnace, water heater or other gas equipment again, have a qualified technician inspect venting, combustion and the heat exchanger.
- Keep the suspected appliance off until it is inspected
- Ask the technician for CO readings in writing
- Replace any alarm older than its stated service life
Prevent CO problems
Prevention is mostly about venting and maintenance.
- Annual furnace inspection before heating season
- Keep flue pipes and outdoor vents clear
- Never run generators, grills or vehicles in a garage or indoors
- Test alarms monthly and follow the replacement date on the label
Questions
Where should CO alarms go?+
Outside each sleeping area and on every level, following the manufacturer's instructions.
How long do CO alarms last?+
Many have a service life of about 5–10 years, printed on the back. Units signal end of life with a chirp or display code.
Can a furnace leak carbon monoxide when it's off?+
An appliance that isn't burning fuel doesn't produce CO, but another appliance, such as a water heater sharing the flue, may still be running. Treat any alarm seriously.
Should I open windows if the CO alarm goes off?+
Get everyone outside first and call 911. Opening windows on the way out is fine, but don't stay inside to ventilate.
Editorial note: this guide is general information for homeowners, not a diagnosis. Desertline Heating & Air is a referral service; a licensed contractor should inspect your equipment before repairs.