How to Carbon Monoxide Detector Check

Carbon monoxide is an invisible, odorless killer that can accumulate from malfunctioning furnaces, water heaters, gas appliances, or attached garage fumes—and you'd never know without a working detector. This life-safety task involves pressing the test button on each CO detector to verify a loud alarm, replacing batteries as needed, and checking manufacture dates since these devices have limited lifespans. Taking a few minutes twice a year to test your CO detectors provides the only warning you'd have of a potentially fatal gas leak.

10 minEasycriticalEvery 180 daysDIY Friendly

Cost to Skip This Task

Risk $5,000 – $500,000 in repairs

Why It Matters

Carbon monoxide is odorless and colorless - you cannot detect it without a working alarm. CO poisoning kills over 400 Americans annually and hospitalizes thousands more. Test every 6 months. Replace batteries annually. Replace the entire detector every 5-7 years regardless of test results—sensors degrade. You need CO detectors on every floor, near bedrooms, and near any fuel-burning appliances.

Safety First

If a CO alarm sounds, immediately evacuate and call 911
CO detectors have a 5-7 year lifespan - check the manufacture date
Place detectors 5 feet above the floor (CO mixes with air but initially rises with warm combustion gases)

What You'll Need

Tools

Step stool0

Supplies

Batteries (9V or AA)$10
Replacement CO detector (if older than 7 years)$25

Step-by-Step Instructions

Before You Start

You should have CO detectors on every floor, near every sleeping area, and near any fuel-burning appliances (furnace, water heater, gas stove, fireplace).

1
Press and hold the test button on each CO detector
2
Verify a loud alarm sounds
3
Replace batteries in any detector that does not alarm loudly
4
Check the manufacture date on each detector - replace if older than 5-7 years
5
Verify detector placement: every floor, near bedrooms, near fuel-burning appliances
6
Ensure detectors are not blocked by furniture or drapes

How to Verify Success

All CO detectors produce a clear alarm when tested. Batteries are fresh. Detectors are within their lifespan. Proper placement verified.

When to Call a Professional

CO alarm sounds during normal use (evacuate immediately, call 911 - fire department responds free)
You need hardwired detectors installed (electrician $50-100 per detector)
You suspect a CO leak but detectors are not triggering (HVAC inspection $100-200, gas company may inspect free)

This guide is part of:

First-Year Homeowner DIY vs Professional