Carbon Monoxide Detector Placement and Monthly Testing
Place CO alarms on each level and outside separate sleeping areas, test them monthly, and know what to do when one sounds, per CPSC.
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Carbon monoxide, or CO, is colorless and odorless, which is why working alarms matter in any home that uses a furnace, a portable heater, or a generator. The U.S. Consumer Product Safety Commission (CPSC) advises placing CO alarms on each level of the home and outside separate sleeping areas, and testing them monthly. This guide covers where each alarm goes, how to test it, and what to do when one sounds.
Summary
The CPSC says to install battery-operated CO alarms, or alarms with battery backup, on each level of the home and outside separate sleeping areas. Interconnected CO alarms are best, because when one sounds, they all sound.
Smoke alarms follow a similar map with one extra stop. The CPSC says to make sure smoke alarms are installed on every level of your home and inside each bedroom.
Test CO and smoke alarms monthly to make sure they are working properly, and replace batteries if needed. If an alarm sounds, do not ignore it. Get outside immediately and call 911.
Alarms are one layer of protection. Where a household runs a portable generator, the CPSC says an average of nearly 100 people die in the U.S. each year from CO poisoning caused by portable generators. Its generator advice is to operate them outside only, at least 20 feet away from the house, with the exhaust directed away.
Alarm Coverage at a Glance
| Place | CO alarm | Smoke alarm |
|---|---|---|
| Every level of the home | Yes, battery-operated or with battery backup | Yes |
| Outside separate sleeping areas | Yes | See the alarm's instructions |
| Inside each bedroom | See the alarm's instructions | Yes |
| Near a furnace or other fuel-burning appliance | Follow the alarm's instructions | Follow the alarm's instructions |
The table shows the main difference between the two alarms in the CPSC advice. CO alarms are placed on each level and outside separate sleeping areas, while smoke alarms are also placed inside each bedroom. Battery backup matters because storms and outages are when generators and heaters often come into use.
Where to Put Each Alarm
Walk your home level by level. A two-story home with a basement has three levels to cover. Put a CO alarm on each level, and put one outside each separate sleeping area, such as the hallway outside the bedrooms. Add smoke alarms to every level and inside each bedroom.
Interconnected alarms are the CPSC's preference. When one sounds, they all sound, which helps when the household is on a different floor from the source.
Follow the alarm's own instructions for mounting height and distance from appliances, because models differ. This guide does not give exact heights or distances for that reason.
How to Test and Maintain Alarms
Test CO and smoke alarms monthly, and replace batteries if needed. Most alarms have a test button, and the instructions that came with yours explain how to use it.
Check the outside vents for fuel-burning appliances too. The CPSC advises clearing snow away from the outside vents for appliances such as furnaces, so that dangerous carbon monoxide does not build up in the house.
| Task | How often | Note |
|---|---|---|
| Press the test button on each CO and smoke alarm | Monthly | Replace batteries if needed |
| Check outside vents of fuel-burning appliances | After snowfall | Clear snow away from the vents |
| Review generator placement | Before it is needed | Outside only, at least 20 feet from the house |
| Replace the alarm itself | On the schedule in its instructions | Follow the manufacturer's replacement date |
When an Alarm Sounds
An alarm is a signal to act. The CPSC says to never ignore an alarm when it sounds. Get outside immediately and call 911.
Share this plan with everyone in the household ahead of time, including visitors who sleep over. If anyone feels unwell, tell the emergency dispatcher when you call.
Generators and Heaters
Keeping CO out of the home comes first, and alarms back that up. The CPSC says to never operate a portable generator inside a home, garage, basement, crawlspace, shed, or other enclosed space. Operate generators outdoors only, at least 20 feet from the house, with the exhaust directed away.
When shopping for a generator, the CPSC advises looking for models with a carbon monoxide shut-off safety feature. It notes that models certified to the latest PGMA G300-2023 and UL 2201-2023 standards include carbon monoxide safety technologies.
Portable heaters have their own rules. Keep all sides of the heater at least three feet from beds, clothes, curtains, papers, sofas, and other items that can catch fire. When using an electric portable heater, always use a wall outlet and never a power strip.
Choosing Order
- Count the levels in your home and the separate sleeping areas on each, then plan one CO alarm per level plus one outside each sleeping area.
- Install the alarms, add smoke alarms inside each bedroom, and choose interconnected models if you can.
- Test every alarm monthly, replace batteries if needed, and keep any generator outside, at least 20 feet from the house.
Before Heating Season
- Walk every level and confirm a working CO alarm is outside each separate sleeping area.
- Press the test button on every alarm and replace any battery that needs it.
- Check that smoke alarms are installed inside each bedroom, not only in the hallway.
- Clear snow from the outside vents of furnaces and other fuel-burning appliances.
- If you own a generator, confirm where it will be run outdoors and whether it has a CO shut-off feature.
- Tell everyone in the household the plan: get outside immediately and call 911 when an alarm sounds.