Where should carbon monoxide detectors be placed, and how many do you need?
Short answer: CPSC advises installing carbon monoxide alarms on every level of the home and outside sleeping areas, with battery power or battery backup. Interconnected alarms are best, because when one sounds, they all sound. Keep alarms out of kitchens, away from heating vents, and not directly above fuel-burning appliances. Follow the manufacturer's placement and replacement instructions.
Where should carbon monoxide detectors go?
The U.S. Consumer Product Safety Commission (CPSC) gives a simple rule. Install CO alarms on every level of the home and outside sleeping areas.
Use battery-operated alarms or alarms with battery backup. CPSC says hardwired and plug-in units should have battery backup, which matters most in a winter outage. Choose an alarm that meets the UL 2034 standard.
CPSC says CO alarms can go in a plug-in outlet or high on the wall. Follow your alarm’s instructions for exact placement.
Where not to put a CO detector
CPSC advises against these spots:
- Kitchens
- Above fuel-burning appliances
- Near heating vents
- Where furniture or drapes could cover the alarm
How many carbon monoxide detectors do you need?
Count one per level, then make sure each sleeping area has one just outside it. If bedrooms are spread across a level, one hallway alarm may not cover them all.
| Home layout | Levels | Separate sleeping areas | Typical minimum |
|---|---|---|---|
| Ranch, bedrooms in one hallway | 1 | 1 | 1 |
| Ranch, split bedroom plan | 1 | 2 | 2 |
| Two-story, bedrooms upstairs, plus basement | 3 | 1 (upstairs) | 3 |
| Two-story, primary suite downstairs, kids upstairs, plus basement | 3 | 2 | 3 |
In the last row, the main-floor alarm sits outside the primary suite and the upstairs alarm outside the kids’ rooms, so 3 covers it.
Your state or city may require more. Check local code before you buy.
Should CO alarms be interconnected?
Yes, if you can. CPSC says interconnected CO alarms are best, because when one sounds, they all sound. A basement alarm is easy to miss from a closed bedroom upstairs. Some smart home systems can also link alarms. See our Matter vs Zigbee vs Z-Wave guide if you are building one.
How to test and when to replace a CO detector
CPSC’s generator safety sheet says to test alarms monthly. CPSC notes the test button only checks the circuitry. It does not prove the sensor is accurate.
CO alarms wear out. CPSC says each alarm has a recommended replacement age, listed in the product literature or available from the manufacturer. Write the install date on the back so you know when it is due.
What are the symptoms of carbon monoxide poisoning?
CO has no color or smell. CPSC lists these symptoms:
| Exposure | Symptoms |
|---|---|
| Low to moderate | Headache, fatigue, shortness of breath, nausea, dizziness |
| High | Confusion, vomiting, loss of muscle coordination, loss of consciousness, death |
Low-level symptoms look like the flu without a fever. If several people in the house feel sick at once, and feel better away from home, suspect CO.
What to do when the CO alarm goes off
Never ignore a CO alarm. CPSC’s steps:
- Get everyone outside to fresh air right away. Don’t stop to hunt for the source.
- Call 911 or the fire department from outside.
- Do a head count so you know everyone is out.
- Do not go back in until emergency responders say it is safe.
If the alarm sounds again within 24 hours, repeat these steps and call a qualified appliance technician.
Common winter sources of carbon monoxide
CPSC estimates about 170 U.S. deaths each year from CO made by non-automotive consumer products. Winter brings several of the main sources:
- Portable generators. Never run one in or near a house, garage, or other enclosed space. CPSC says open doors and windows do not prevent deadly CO buildup. Its generator sheet says to run them outside, at least 20 feet from the house, away from windows, doors, and vents. A battery power station makes no exhaust; see power station vs generator and winter power outage preparation.
- Furnaces and other fuel-burning appliances. CPSC advises a professional inspection and service of the heating system every year, plus checking chimneys and flues for blockages.
- Cars in attached garages. Never leave a car running in an attached garage, even with the door open.
- Charcoal. Never burn charcoal inside a home, garage, vehicle, or tent.
Add a furnace check and fresh alarm batteries to your winterizing checklist.
Quick answers
Do I need a carbon monoxide detector on every floor? Yes. CPSC recommends a CO alarm on every level of the home, plus outside sleeping areas.
What should I do if my CO alarm goes off? Get everyone outside to fresh air and call 911. Do not go back in until emergency responders say it is safe.