Replace your carbon monoxide alarm every 5 to 7 years, or sooner if it fails a test or stops responding

Most carbon monoxide detectors have a lifespan of 5 to 7 years. After that, the sensor inside degrades and may not detect carbon monoxide reliably, even if the alarm appears to work. Check the back or bottom of your unit for a manufacture date printed directly on the device — that's your starting point. If you can't find a date, assume the alarm is older than you know and replace it now.

Some alarms have an end-of-life indicator: a beeping pattern that's different from the alarm sound itself, or a light that blinks in a specific way. Check your manual or the manufacturer's website to learn what your model does when it reaches the end of its useful life. If your alarm beeps four times in a row every 30 seconds, that's usually the end-of-life signal — not a carbon monoxide warning.

Key Takeaways

  • Replace your carbon monoxide alarm 5 to 7 years after manufacture, regardless of whether it appears to work.
  • The manufacture date is printed on the back or bottom of the unit; if you cannot find it, replace the alarm when ready.
  • A four-beep pattern every 30 seconds usually means the alarm has reached end of life and needs replacement, not that carbon monoxide is present.
  • Test your alarm monthly using the test button; if it does not sound, replace it right away.
  • Battery-powered alarms need fresh batteries twice a year; hardwired alarms with battery backup need the backup battery replaced annually.

Why carbon monoxide sensors wear out

The sensor inside a carbon monoxide alarm is a chemical element that reacts to carbon monoxide gas. Over years of exposure to air and humidity, that element degrades. It doesn't fail suddenly — it just becomes less sensitive. An alarm that's 8 or 10 years old might miss low levels of carbon monoxide that a new alarm would catch when ready.

This degradation happens whether the alarm has ever detected carbon monoxide or not. A perfectly quiet alarm in a safe home still needs replacement on schedule. The sensor doesn't "wear out" from use; it wears out from time.

How to find the manufacture date on your alarm

Turn off the alarm or remove it from the wall. Look at the back, bottom, and sides of the unit for a date printed directly on the plastic or label. It may say "Manufactured" or "MFG" followed by a month and year. Some manufacturers use a code instead — for example, a number like "0821" meaning August 2021.

If the date is hard to read or you're unsure of the format, take a photo and search the manufacturer's website for how to decode their date stamps. You can also call the manufacturer's customer service line with the model number (usually on the front or back) and they'll tell you the age.

If you find no date anywhere on the unit, or if the alarm is older than 5 years, replace it. There's no safe way to know if an undated alarm is still reliable.

Testing your alarm monthly and replacing it if it fails

Press and hold the test button on your alarm for 3 to 5 seconds. The alarm should sound loudly within a few seconds. If nothing happens, or if the sound is very faint, the alarm is not working properly and needs replacement when ready — don't wait for the 5-year mark.

Test your alarm on the first of each month so you build a habit. Write the test date on a calendar or set a phone reminder. If the test fails, buy a replacement that day. A non-functioning alarm offers no protection.

Battery replacement versus full alarm replacement

A battery-powered carbon monoxide alarm (one that runs entirely on AA or 9-volt batteries) needs fresh batteries twice a year — for example, when you change your clocks for daylight saving time. Replace the batteries even if the old ones still have some charge left. A low battery might prevent the alarm from sounding in an emergency.

A hardwired alarm (plugged into your home's electrical system) usually has a battery backup for power outages. Replace that backup battery once a year, typically in spring or fall. The backup battery is separate from the main power supply and degrades on its own schedule.

Neither of these battery replacements extends the life of the alarm itself. After 5 to 7 years, you still need to replace the entire unit, batteries and all.

Where to buy a replacement alarm

Carbon monoxide alarms are sold at hardware stores, home improvement retailers, and online marketplaces. Look for an alarm that meets the UL 2034 standard (printed on the box or manual) — this is the safety standard for carbon monoxide detectors in North America. Most alarms in stores meet this standard, but it's worth checking.

Choose either a battery-powered model or a hardwired model depending on what you're replacing. If you're unsure whether your current alarm is hardwired or battery-powered, look at the back: a hardwired alarm has a plug or wires, while a battery-powered one has a battery compartment.

Installing your new alarm in the same location

Install the new alarm in the same spot as the old one. Carbon monoxide detectors work best on a wall 4 to 6 feet above the floor, or on a ceiling, in a central location where you'll hear it from any room. Avoid placing it near windows, doors, or vents where drafts can interfere with the sensor.

If your old alarm was hardwired, the new one should be too — the wiring is already in place. If you're uncomfortable working with electrical wiring, call a licensed electrician to install it. If your old alarm was battery-powered, straightforward insert fresh batteries into the new unit and mount it on the wall using the included hardware.

Test the new alarm when ready after installation to confirm it works.

Frequently Asked Questions

What does it mean if my alarm beeps four times every 30 seconds?

That pattern usually signals end of life, not carbon monoxide. Check your manual to confirm. If it is the end-of-life signal, replace the alarm. If you're unsure, test the alarm with the test button — if it sounds normally during the test, the four-beep pattern is likely end of life.

Can I just replace the battery instead of the whole alarm?

No. Replacing the battery extends the alarm's power supply but not the lifespan of the sensor itself. After 5 to 7 years, the sensor degrades regardless of battery age. You must replace the entire unit.

My alarm is 3 years old and works fine. Do I really need to replace it yet?

Not yet. If the test button works and the alarm is under 5 years old, it's still reliable. Mark the manufacture date on your calendar so you remember to replace it when it reaches 5 years. Test it monthly in the meantime.

What if I don't know how old my alarm is?

If you cannot find a manufacture date anywhere on the unit, replace it now. You cannot safely assume it's still working if you don't know its age.

Should I replace all my alarms at the same time?

Yes, if they were all installed around the same time. Replacing them together means you won't have to remember different replacement dates for different alarms. If some are newer than others, replace the oldest ones first and stagger the rest.