Replace a carbon monoxide alarm by the end-of-life date on its label. The CDC says to follow the manufacturer's instructions or replace it every 5 years. In between, test it monthly, change replaceable batteries once a year, and make sure there's one on every level of the home and outside each sleeping area (CPSC).
Carbon monoxide has no color or smell, so an alarm is the only warning most people get. The CDC counts more than 400 deaths in the US each year from accidental CO poisoning not linked to fires, plus more than 100,000 emergency department visits. CO alarms sit alongside smoke alarms, so the monthly test belongs in the same routine: see how often to test and replace smoke detectors.
How to tell how old it is
- Read the label. The back or side shows a manufacture date, and your manual gives the model's service life. If you can't find or read the date, First Alert says replacing the alarm is the safer choice.
- Listen for the end-of-life chirp. Kidde says CO alarms give an end-of-life chirp after 7 to 10 years of power, depending on the model. On some Kidde models it starts seven years after first power-up and repeats every 30 seconds, and the alarm no longer senses CO in that state.
- Don't trust the test button alone. First Alert says to replace a CO alarm on its recommended timeline even if it still powers on and passes its test.
The CDC suggests setting a calendar reminder for the replacement date when you install a new alarm. Writing the install date on the alarm with a marker helps too.
Where to put CO alarms
- On every level of the home (CPSC, U.S. Fire Administration).
- Outside each sleeping area, in a central spot (U.S. Fire Administration). The CDC puts it as near every sleeping area. They mean the same thing: close enough to wake people.
- Not in attics or basements unless someone sleeps there (CPSC).
- Mounting height and distance from appliances: follow your alarm's installation instructions (CPSC).
The CDC recommends battery-powered alarms or ones with battery backup, so they keep working in a power cut.
Who needs one
CO comes from fuel that doesn't burn completely. The U.S. Fire Administration names furnaces, heaters and generators that aren't working or vented properly. You need CO alarms if your home has any of these:
- A gas, oil or wood-burning furnace, boiler, water heater, stove or dryer.
- A fireplace or wood stove.
- An attached garage. The CDC says never to run a car in an attached garage, even with the door open.
- A portable generator you use in outages. The CDC says to run it outside, more than 20 feet from windows, doors and vents, and to have a battery or battery-backup CO alarm inside.
Airbnb strongly urges hosts with fuel-burning appliances to install smoke and CO alarms and test them regularly, and notes that local rules may require more than one. Rules vary by place, so check yours. More for hosts is on our page for short-term rental hosts.
Testing and batteries
- Test every CO alarm once a month with its test button (CPSC).
- Replace replaceable batteries once a year (CPSC). The CDC suggests checking them when the clocks change in spring and fall.
- Sealed alarms have no battery to change. You replace the whole unit at end of life.
- Have fuel-burning heating, water heaters and chimneys checked by a qualified technician each year (CDC). That's the job that stops CO at the source. Our seasonal home maintenance checklist puts it in the fall.
What to do if it goes off
A full CO alarm is a loud, repeating pattern. CPSC's advice:
- Get outside into fresh air right away.
- Make sure everyone else in the home gets out too.
- Call 911 or the fire department from outside, not from inside the house.
- Stay outside until help arrives.
CO poisoning feels like the flu: headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion (CDC). People who are asleep can die before they notice any symptoms, which is why the alarms go near bedrooms. If anyone feels ill, tell the 911 operator.
Chirps and beeps that aren't an emergency
First Alert is clear that a short chirp does not mean the alarm has found carbon monoxide. On Kidde CO alarms, a low battery chirps once every 60 seconds, and a chirp every 30 seconds can mean end of life or a fault. Other brands differ, so check your manual. CPSC suggests learning the difference between your smoke alarm's sound and your CO alarm's sound before you ever need it.
Combination smoke and CO alarms
Combined smoke and CO alarms are available (CPSC). They cover both jobs in one unit, but you still need smoke alarms in every bedroom, which is more places than CO alarms need. Replace a combination alarm by the date on its label, and follow its manual for where it goes.
CO alarm placement and schedule (printable)
| Check | Done? |
|---|---|
| Basement: alarm only if someone sleeps there, or follow your manual | |
| Main floor: one CO alarm on this level | |
| Upstairs: one in a central spot outside the bedrooms | |
| Separate sleeping area (in-law suite, finished attic room): one outside it | |
| Replace-by date written down for every alarm |
| Job | How often |
|---|---|
| Press the test button on every CO alarm | Monthly |
| Replace replaceable batteries | Once a year |
| Fuel-burning heating, water heater and chimney checked | Once a year |
| Replace the alarm | By the label date (CDC: per the maker, or every 5 years) |
Questions people ask
Do carbon monoxide detectors expire?
Yes. The sensor wears out, so replace the alarm by the end-of-life date on its label. The CDC says to follow the manufacturer's instructions or replace it every 5 years.
Where shouldn't a CO detector go?
CPSC says not in attics or basements unless someone sleeps there. Follow your alarm's manual for anything else, such as distance from fuel-burning appliances.
How high should a CO detector be mounted?
Follow the installation instructions for your model. Wall, ceiling and plug-in models each have their own guidance.
Do I need a CO detector if I don't have gas?
You do if you have any fuel-burning appliance, a fireplace, an attached garage or use a portable generator. Airbnb lets hosts with only electric appliances and no attached garage mark a CO alarm as not needed, but local rules may still require one.
What should I do if my CO alarm goes off?
Get everyone outside into fresh air right away, call 911 or the fire department from outside, and stay out until help arrives (CPSC).
Why is my CO detector beeping?
A short chirp usually means a low battery or the end of its life, not carbon monoxide. A loud, repeating alarm means get out. Our smoke detector chirping guide covers chirps in more detail.
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Sources
- CDC: Carbon monoxide poisoning basics
- CPSC: Carbon monoxide alarms
- CPSC: Carbon monoxide alarms mini lesson (PDF)
- U.S. Fire Administration: Carbon monoxide
- Kidde: What causes consistent chirping?
- Kidde: Why do smoke alarms always chirp in the middle of the night?
- First Alert: Why is my carbon monoxide alarm chirping?
- Airbnb Help Center: Smoke and carbon monoxide alarms (article 514)
General guidance only. Follow your manufacturer's instructions, and call a licensed professional for gas, electrical, roofing or anything that feels unsafe.