How to Check Carbon Monoxide Detectors

Carbon monoxide doesn’t give you a second chance. It’s called the silent killer because you can’t see it, smell it, or taste it. By the time you feel symptoms—headache, dizziness, nausea—you might already be too disoriented to get out. That’s why CO detectors matter. But only if they work.

Why This Matters

Every year in the US, carbon monoxide poisoning sends more than 50,000 people to the emergency room and kills over 400. The sources are common:

• Gas furnaces and water heaters
• Wood stoves and fireplaces
• Gas stoves and ovens
• Attached garages (car exhaust)
• Portable generators
• Charcoal grills used indoors

A working CO detector is your only early warning. No detector, no warning, no second chance.

The Monthly Test

It takes ten seconds. Press and hold the test button on each detector. You should hear a loud alarm. If you don’t, the detector isn’t working—replace it immediately.

Do this for every detector in your home. Not just one. All of them.

What to Check

1. Test Button

Press it. It should alarm loudly within a few seconds. No sound means dead batteries, expired unit, or malfunction.

2. Batteries

Even hardwired detectors have backup batteries. Replace them twice a year—do it when you change your clocks for daylight saving time. It’s an easy habit.

3. Expiration Date

CO detectors don’t last forever. Most have a 5-7 year lifespan. Check the manufacture date on the back or the expiration label. If it’s expired, replace it. No exceptions.

Some units beep or flash to indicate end of life. Others just stop working silently.

4. Placement

Your detectors need to be in the right places:

• Every level – Basement, main floor, upstairs, attic if used
• Near bedrooms – Within 10 feet of sleeping areas so you’ll hear it
• On the wall or ceiling – CO mixes with air, so height doesn’t matter as much as smoke
• Away from false alarms – Not right next to fuel-burning appliances

5. Clean and Clear

Dust can clog sensors. Once a month when you test, give each detector a quick vacuum or wipe. Don’t paint over them or cover them.

Signs Your Detector Needs Replacing

• Won’t respond to test button
• Beeps intermittently (not the low-battery chirp)
• Is past its expiration date
• Shows error codes or fault lights
• Has been exposed to high CO levels (after an incident)

What to Do If It Alarms

Don’t second-guess it. Don’t assume it’s a false alarm. Take action:

1. Get everyone out immediately – Pets too
2. Leave doors open – Helps ventilate
3. Call 911 from outside – Let professionals check it out
4. Don’t go back in – Until emergency responders clear it
5. Get fresh air – If anyone has symptoms, seek medical attention

Symptoms of CO poisoning: headache, dizziness, nausea, confusion, chest pain. If anyone experiences these, it’s a medical emergency.

DIY vs. Call a Pro

DIY: Testing detectors, replacing batteries, checking expiration dates, installing battery-powered units.

Call a pro: Hardwired installation, interconnected systems, troubleshooting nuisance alarms, HVAC inspection if you suspect CO problems. Find an electrician →

How Often to Check

• Monthly: Press the test button on every detector
• Twice yearly: Replace batteries (even hardwired backup batteries)
• Yearly: Check expiration dates on all units
• Every 5-7 years: Replace detectors proactively

The Bottom Line

Carbon monoxide detectors are cheap insurance. A decent one costs less than dinner out. Test them monthly, replace the batteries, and toss them when they expire. It’s the simplest thing you can do to protect your family from something that gives no warning.