How to test and add carbon monoxide alarms
For carbon monoxide alarm placement, pick a central spot outside each sleeping area and on every level, then test each alarm monthly. Use alarms meeting UL 2034, with batteries or battery backup. Keep them away from vents and out of kitchens. If one sounds, go outside and call 911.
Which carbon monoxide alarm to buy
You can't see or smell carbon monoxide, and early symptoms feel like flu without the fever. Only an alarm will tell you. Federal data cited by NFPA puts the toll at about 101,847 ER visits, 14,365 hospital stays and at least 430 deaths a year from unintentional CO poisoning not related to fires.
CPSC says to buy alarms that meet the current UL 2034 standard and run on batteries or have a battery backup, so they work in a power cut. That's when generators and improvised heating raise the risk. Look for a recognized testing lab's label on the package.
Combination smoke and CO alarms are sold too. They save ceiling space, but they mean both functions expire at once, so replace the unit on the date the maker gives. Interconnected alarms are best, because when one sounds they all do. You'd want this for a basement furnace and a bedroom two floors up.
CPSC recommends CO alarms outside bedrooms even in homes with no fuel-burning appliances. An attached garage or a neighbor's generator can bring the gas in.
Where to put a carbon monoxide detector
NFPA's guidance is a central location outside each sleeping area, on every level, and anywhere else your local code requires. Follow the manufacturer's instructions for mounting height, because models differ.
CPSC adds these limits:
- Not in a kitchen or directly above a fuel-burning appliance.
- Not near heating vents.
- Not where furniture or curtains could cover the alarm.
- Not in attics or basements unless someone sleeps there, according to one CPSC page. Another CPSC page says every level, so if your basement holds a furnace, follow the alarm's manual and your local code.
State and local rules on CO alarms vary. Ask your local fire department or building department what applies to your home.
How to test a carbon monoxide alarm and fill the gaps
- Find your sources
Note every fuel-burning appliance, the fireplace and any attached garage, so you know where the risks are.
- Test what's already there
Press the test button on each CO or combination alarm. Test monthly from now on.
- Check the replacement date
Read the label and the manual for the replacement age. Replace anything past it, or anything showing an end-of-life signal.
- Fill the gaps
Add alarms outside each sleeping area and on every level. Keep them clear of vents, kitchens and furniture.
- Add the fire department's number
NFPA suggests calling the non-emergency line now to learn which number to call if a CO alarm sounds.
- Agree on the alarm plan
Everyone goes outside to fresh air and does a head count. Call 911 from outside. Nobody goes back in until responders say it's safe.
- Book the heating service
Have a pro inspect your heating system each year, and check the chimney and flues for blockages and loose connections. If the alarm sounds again within 24 hours of going back in, leave again and have a qualified technician check all fuel-burning equipment.
What a carbon monoxide alarm costs
| Item | What it costs | Notes |
|---|---|---|
| Battery CO alarm | Varies by brand | One per level and sleeping area at minimum |
| Combination smoke and CO alarm | More than a single-purpose unit | Check replacement age on the label |
| Hardwired or interconnected setup | Varies; get an electrician's quote | Have a qualified electrician do the wiring |
| Yearly heating system service | Varies by area and fuel | CPSC says to do this every year |
Carbon monoxide alarm placement and testing mistakes
- Trusting the test button too much. CPSC says it checks the circuitry, not the sensor's accuracy. Replace any alarm past its date, even if it beeps.
- Going looking for the source when the alarm sounds. Get out first.
- Waving off an alarm because nobody feels ill. Fire departments respond to thousands of real CO incidents a year, and symptoms are easy to miss.
- Restarting a suspect appliance. Leave it off until trained personnel have serviced it.
- Running a car in the attached garage, even with the door open.
What homeowners say about carbon monoxide detector placement
Read the manual and learn your alarm's beep patterns. On one owner's unit, four beeps means CO and three means smoke. They taped a short what-to-do card inside a kitchen cabinet. If the alarm goes off and you can't see smoke, assume it may be CO and get everyone out. (Reddit)
Carbon monoxide alarm placement questions
Where should a carbon monoxide alarm be placed?
In a central spot outside each sleeping area and on every level, following the manual for height. Keep it out of kitchens, away from heating vents and away from directly above fuel-burning appliances.
What does the test button on a CO alarm check?
CPSC says the button checks the circuitry, not how accurately the sensor reads CO. That's why the replacement date matters as much as a passing test.
Do I need a CO alarm if my house is all electric?
CPSC recommends one outside bedrooms even without fuel-burning appliances. Cars in attached garages and generators running nearby can still produce CO. Check your state and local code, too.
What you’ll need
General guidance for U.S. homes, not professional advice. For gas, electrical and structural work, call a licensed pro.