When to Replace Carbon Monoxide Detectors
Everything you need to know about the lifespan, warning signs, and replacement timeline for carbon monoxide detectors.
The Short Answer
Replace carbon monoxide detectors every 5 to 7 years, depending on the manufacturer's recommendation. CO detectors have a shorter lifespan than smoke detectors because their electrochemical sensors degrade faster. Check the manufacture date on the back of the unit.
Why Carbon Monoxide Detectors Need Replacing
Carbon monoxide detectors rely on electrochemical sensors that contain a chemical gel. When carbon monoxide molecules contact this gel, it produces a small electrical current that triggers the alarm. Over time, the gel dries out and loses its ability to detect CO molecules accurately.
Unlike smoke detectors, CO detectors cannot be restored by cleaning. The chemical reaction that makes detection possible is a consumable process. Even in a home that never experiences a CO event, the sensor chemistry degrades from normal exposure to ambient air.
Carbon monoxide is colorless, odorless, and tasteless. It is impossible to detect without a working sensor. The CDC reports that over 400 Americans die from unintentional CO poisoning each year, and more than 100,000 visit emergency rooms. A detector with a degraded sensor provides a dangerous false sense of security.
Warning Signs It's Time to Replace
- The unit displays an "End of Life" or "EOL" message (many modern units include this feature)
- Persistent chirping that continues after a fresh battery is installed
- The digital display (on models with one) shows erratic readings
- The test button produces no response or a weak tone
- The unit is more than 5 years old (check the manufacture date)
- Physical damage, cracks, or discoloration on the housing
How to Check the Age of Your Carbon Monoxide Detectors
Look at the back of the detector for a manufacture date label. Most CO detectors print the date clearly (e.g., "MFG 06/2021"). Many newer models also display a "Replace By" date. Some models have a digital display that will show an "End" or "Err" code when the sensor has reached end of life. If no date is visible, check the model number against the manufacturer's website.
Replacement Recommendations
Choose a CO detector that meets UL 2034 standards. Plug-in models with battery backup offer continuous protection even during power outages. Digital display models show real-time CO levels, which helps you identify low-level exposure before the alarm threshold is reached. For homes with attached garages, place a detector on the wall shared with the garage. Combination smoke and CO detectors can simplify installation but must still be replaced on the shorter CO detector timeline.
The Bottom Line
Carbon monoxide detectors should be replaced every 5 to 7 years per manufacturer guidelines. The electrochemical sensor is consumable and cannot be repaired or refreshed. Install at least one CO detector on every level of your home and near sleeping areas. Test monthly. If your home uses any combustion fuel source (gas, oil, propane, wood) or has an attached garage, working CO detectors are essential.
Frequently Asked Questions
Install CO detectors on every level of your home, including the basement. Place one near each sleeping area so the alarm will wake you. Install them at least 15 feet from fuel-burning appliances to avoid false alarms during normal startup. Wall-mounted units should be placed at knee height to waist height, since CO mixes with air evenly but this height catches rising warm air from common sources.
Yes. The electrochemical sensor degrades from normal air exposure, not from alarm events. A CO detector that has never sounded an alarm degrades at the same rate as one that has. The chemical gel that enables detection dries out and loses sensitivity over time regardless of use.
Yes, combination units are convenient and save installation space. However, be aware that the CO sensor typically expires before the smoke sensor. A combination unit should be replaced on the shorter CO detector timeline (5-7 years), even though the smoke sensor might still have years of life remaining.