How to Test and Replace Carbon Monoxide Detectors
Carbon monoxide is called the "silent killer" for good reason — it's colorless, odorless, and tasteless. Over 400 Americans die from unintentional CO poisoning each year. Properly placed and maintained CO detectors are your only warning system.
Time Required
10-15 minutes
Difficulty
Easy
Tools Needed
Fresh batteries, screwdriver
CO Safety Warning
If your CO alarm is currently sounding, do not stay to troubleshoot. Get everyone out of the house immediately, including pets. Call 911 from outside. Carbon monoxide poisoning symptoms — headache, dizziness, nausea — mimic the flu, making it easy to dismiss until it's too late.
Understanding CO Detector Lifespan
CO detectors expire sooner than most homeowners realize. The electrochemical sensor inside actively consumes a chemical reagent as it monitors for carbon monoxide, even when no CO is present.
- 5-7 year lifespan: Most standard CO detectors use an electrochemical sensor rated for 5-7 years. After that, the sensor loses sensitivity and may not detect dangerous CO levels. Check the date printed on the back of your unit.
- 10-year sealed units: Some premium models (like Kidde 10-Year or First Alert 10-Year) use a longer-lasting sensor and sealed lithium battery. These still must be replaced at 10 years.
- End-of-life chirp: Most CO detectors emit a specific chirp pattern (different from a low-battery chirp) when the sensor has expired. Consult your model's manual to distinguish between battery chirps and end-of-life chirps.
- Date code location: The manufacture date is typically printed or stamped on the back of the unit. If you can't find a date, assume the unit needs replacement.
Proper Placement for CO Detectors
Near sleeping areas
Install a CO detector within 15 feet of each bedroom door. CO poisoning is most dangerous at night because victims inhale the gas while sleeping and may never wake up. This placement ensures the alarm is loud enough to wake occupants.
On every level of the home
Each floor needs at least one CO detector, including the basement (especially if it contains a furnace, boiler, or water heater). CO rises with warm air currents and can accumulate on upper floors even if the source is in the basement.
Near fuel-burning appliances (but not too close)
Place detectors in the same room as furnaces, water heaters, fireplaces, and attached garages, but at least 15 feet away from the appliance. Being too close causes nuisance alarms from normal startup combustion byproducts.
Common CO Sources in Your Home
- Furnaces and boilers: A cracked heat exchanger is the most common source of household CO. The crack allows combustion gases to mix with the heated air flowing into your living spaces.
- Water heaters: Gas water heaters with backdrafting flues can push CO into the home instead of venting it outside. Check that the draft hood draws air upward when the burner is running.
- Attached garages: A car idling in an attached garage can fill the home with CO within minutes, even with the garage door open. Never warm up a vehicle in an attached garage.
- Generators and grills: Portable generators and charcoal grills produce massive amounts of CO. Never operate them indoors, in a garage, or near open windows.
- Blocked chimneys and flues: Bird nests, debris, or structural damage can block the exhaust path for fireplaces, furnaces, and water heaters, causing CO to back up into the home.
CO Alarm Response Procedure
Get everyone out immediately
Move all people and pets to fresh outdoor air. Do not waste time opening windows or searching for the source. Every second of continued exposure increases the danger.
Call 911 from outside
Report a carbon monoxide alarm. The fire department will respond with CO monitoring equipment to measure levels throughout the home and identify the source.
Seek medical attention if symptomatic
If anyone has headaches, dizziness, nausea, or confusion, tell the 911 operator. These are signs of CO poisoning and may require oxygen therapy or hyperbaric treatment. Symptoms can worsen even after leaving the contaminated area.
Pro Tips
- •CO detectors with digital displays are worth the upgrade: Models with PPM (parts per million) readouts let you monitor low-level CO that wouldn't trigger an alarm but could indicate a developing problem with an appliance.
- •Combination smoke/CO detectors simplify maintenance: Units like the First Alert SCO501CN combine both sensors in one device, reducing the number of units to test and maintain. Just remember they still follow the shorter CO sensor lifespan.
- •Test CO detectors with the button, not with actual CO: Never use car exhaust or other CO sources to test a detector. The test button simulates the sensor response electronically and is the manufacturer-approved testing method.
- •All-electric homes still need CO detectors: Even without gas appliances, CO can enter from an attached garage, a neighbor's unit in a condo, or a portable generator used during a power outage.