Replace your carbon monoxide detector every 5 to 7 years, or sooner if it fails a test or stops responding
Most carbon monoxide (CO) detectors have a lifespan of 5 to 7 years. After that, the sensor inside degrades and may not detect dangerous levels of carbon monoxide reliably. Check the back or bottom of your detector for a manufacture date — if it's older than 7 years, replace it now, even if it seems to be working.
Some detectors have a built-in expiration date printed directly on the unit. Others show only the manufacture date, which is when you start counting. If you can't find either date, assume the detector is at least 5 years old and replace it to be safe.
Don't wait for the detector to fail. A detector that stops beeping or shows a low-battery warning may have a failing sensor, not just a dead battery. If replacing the battery doesn't restore normal operation, the detector itself needs to go.
Key Takeaways
- Replace any CO detector that is 7 years old or older, regardless of whether it appears to work.
- Check the manufacture date on the back or bottom of the unit; if you can't find a date, replace it as a precaution.
- A detector that fails a self-test, stops chirping after a battery change, or shows a fault light should be replaced when ready.
- Some detectors have a built-in expiration date; follow that date if it is printed on the unit.
- Keep a record of when you installed each detector so you know when replacement is due.
How to find the manufacture date on your detector
The manufacture date is usually stamped on the back of the unit or on the bottom edge. It may be printed as a date code — for example, "MFG 03/2019" or "Made 2020" — or as a full date like "March 2019." Some detectors use a Julian date code (a number from 1 to 365 representing the day of the year), which is harder to read but still tells you the year.
If the detector is mounted on a wall or ceiling, you may need to remove it to see the date. Most detectors pull straight down or twist counterclockwise to release from the mounting bracket. Write down the date before you put it back, or take a photo of the label so you have it for your records.
If the date is worn off or illegible, or if you inherited the detector with the house and have no installation record, replace it. The cost of a new detector is far less than the risk of a missed carbon monoxide leak.
Signs your detector needs replacement before 7 years
A detector that fails its self-test should be replaced when ready. Most units have a test button on the front. Press and hold it for 3 to 5 seconds — the alarm should sound. If it doesn't, the sensor may be failing. Replace the detector even if it's only a few years old.
A detector that chirps every 30 to 60 seconds usually signals a low battery. Replace the battery first — use the exact type listed in the manual, usually a 9-volt or AA/AAA set. If the chirping continues after a fresh battery, the detector's sensor is likely failing and the unit should be replaced.
Some detectors have a "fault" or "end of life" light that blinks periodically. This is the manufacturer's signal that the sensor is degrading and replacement is needed. Don't ignore it — the detector may still alarm, but its reliability is declining.
What to do when you replace a detector
Turn off power to the detector at your circuit breaker if it is hardwired. Remove the old unit from its mounting bracket and disconnect any wiring. Install the new detector in the same location — typically near bedrooms, in hallways, or in the kitchen, but not directly above a stove or in a very humid area.
If the new detector is battery-powered, insert fresh batteries before mounting. If it is hardwired, connect the wires to the terminals (usually marked positive and negative or red and black) and restore power at the breaker. Test the new detector when ready by pressing the test button — the alarm should sound within 3 to 5 seconds.
Write the installation date on the back of the new detector with a permanent marker, or keep a home maintenance log listing each detector's location and install date. This makes it straightforward to know when replacement is due without having to search for the manufacture date again.
Hardwired versus battery-powered detectors
A hardwired detector is connected to your home's electrical system and usually has a battery backup. These are common in newer homes and in homes where detectors are required by code. Hardwired detectors don't need battery changes, but they still have a sensor lifespan of 5 to 7 years. When you replace one, you'll need to disconnect the wires and reconnect them to the new unit — a straightforward task if you're comfortable working with electrical connections, or a job for an electrician if you're not.
A battery-powered detector runs entirely on batteries and is easier to install — just mount it on a wall or ceiling and insert batteries. These are common in rental homes and in rooms far from the electrical panel. Battery-powered detectors need a battery change once or twice a year, depending on the model. The sensor still expires after 5 to 7 years, so you'll replace the entire unit, not just the batteries.
Some homes have both types. If you're unsure whether a detector is hardwired, look for wires coming out of the back. If there are no wires, it's battery-powered.
Keeping track of multiple detectors
Most homes need at least one CO detector, and many have several — one near the bedrooms, one in the kitchen, and one near the furnace or water heater. Keeping track of when each one expires can be confusing, especially if they were installed at different times.
Create a straightforward list or spreadsheet with the location of each detector, its install date, and its replacement date. Tape a copy to the inside of a kitchen cabinet or your home maintenance binder. Set a phone reminder for a month before the replacement date so you have time to order a new detector and install it without rushing.
Alternatively, replace all detectors on the same schedule — for example, every January — even if some are only 5 years old. This simplifies maintenance and ensures none are overlooked.
When to call a professional
If your detector is hardwired and you're not comfortable working with electrical connections, hire an electrician to disconnect the old unit and install the new one. The job usually takes 15 to 30 minutes per detector and costs less than a service call for a heating or plumbing problem.
If you detect carbon monoxide in your home — the detector alarms and you smell a rotten-egg odor or feel dizzy or nauseous — leave when ready and call 911 from outside. Do not try to locate the source yourself. Once the fire department has cleared the home, a heating technician can inspect your furnace, water heater, and appliances to find the leak.
Frequently Asked Questions
Can I just replace the battery instead of the whole detector?
No. The battery powers the detector, but the sensor inside has a separate lifespan of 5 to 7 years. After that, the sensor degrades and may not detect carbon monoxide reliably, even with a fresh battery. You must replace the entire unit.
What if I don't know how old my detector is?
Look for a manufacture date on the back, bottom, or inside edge of the unit. If you can't find one or it's illegible, replace the detector. It's not worth the risk to guess. A new detector costs $30 to $100, far less than the danger of a missed carbon monoxide leak.
Do I need to turn off power before replacing a hardwired detector?
Yes. Turn off the breaker that controls the detector before you disconnect any wires. This prevents electrical shock and damage to the wiring. If you're unsure which breaker controls the detector, turn off the main breaker or call an electrician.
Can I install a new detector in a different location?
Yes, but follow the manufacturer's guidelines. CO detectors should be near bedrooms, in hallways, or on each level of the home. Avoid direct sunlight, high humidity, and areas above stoves or near fireplaces. If you're moving a detector, check the manual for the recommended placement.
What should I do with the old detector?
Most detectors can be thrown away with regular trash, but check your local waste guidelines — some areas have special disposal rules for electronic devices. Do not try to disassemble or repair the old detector. If it's still under warranty and failed prematurely, contact the manufacturer about a replacement.