Do carbon monoxide detectors expire, and how often should you replace them?

Short answer: Yes — carbon monoxide detectors expire. The electrochemical sensor inside has a finite working life, so you replace the whole alarm on the manufacturer's schedule: older units roughly every 5 to 7 years, and many current sealed 10-year models at 10 years. UL 2034 is the governing U.S. standard and now requires an end-of-life signal. The clock starts at the date of manufacture printed on the back, not the day you installed it.

Do carbon monoxide detectors expire? Sensor life and replacement (2026 Guide)

A carbon monoxide detector is a chemical instrument, not a passive bracket, and like any sensor it wears out. The detection element in nearly every residential unit is an electrochemical CO sensor whose response slowly drifts and degrades over years of exposure to ordinary air, humidity, and trace contaminants — which is why a carbon monoxide alarm carries an expiration date even if it has never once gone off. The controlling U.S. standard is UL 2034, Standard for Single and Multiple Station Carbon Monoxide Alarms, and current editions require the alarm to give a distinct end-of-life warning so the homeowner knows when sensor life is exhausted.

This guide explains how long a carbon monoxide detector lasts, why the older 5-to-7-year units gave way to today's sealed 10-year alarms, and how to read the manufacture date so you replace on time. Because carbon monoxide is invisible and odorless, an expired or silently failed alarm is a real hazard — the U.S. Consumer Product Safety Commission attributes hundreds of accidental CO deaths each year to exposure in the home. Whether you run a single CO detector or a whole-house set, knowing the expiration rule is basic home safety.

Why this matters.
An expired carbon monoxide detector can read normal while no longer reliably detecting a dangerous gas you cannot see or smell. UL 2034 now mandates an end-of-life warning precisely because a silently dead sensor offers false reassurance; CPSC and fire authorities recommend replacing the entire alarm on the manufacturer's stated schedule rather than only swapping the battery. The CPSC carbon monoxide center reports that unintentional CO poisoning causes well over 400 deaths a year in the United States, many in homes where alarms were missing, disabled, or past their service life.

Part 1 — Yes, CO detectors expire: what actually wears out

The short answer is unambiguous: carbon monoxide detectors expire and must be replaced as a whole unit on a fixed schedule. The component that ages is the gas sensor, not the housing or the horn. Understanding why the sensor has a limited life makes the replacement rule easier to follow.

The electrochemical sensor has a finite life

Almost all residential carbon monoxide alarms use an electrochemical sensor — a small cell whose chemistry reacts to CO and produces a measurable current. That chemistry is consumed and drifts over time even in clean air, so the sensor gradually loses accuracy and eventually can no longer be trusted to detect dangerous concentrations. Manufacturers set a service life that the sensor is validated to meet, and that is the alarm's expiration.

It is the alarm, not the battery, that expires

A common mistake is treating a chirping alarm as a dead battery. Replacing the battery does not reset the sensor. When the unit reaches end of life, the correct action is to replace the entire alarm. On a sealed 10-year unit, the lithium battery and the sensor are both designed to last the life of the unit and are not user-serviceable, so the whole device is discarded and replaced at expiration.

Part 2 — How long does a carbon monoxide detector last?

Lifespan depends on the generation and model of the alarm. The industry shifted from replaceable-battery units with shorter sensor lives to sealed long-life units, and the difference matters when you are deciding whether to replace or keep an older detector.

Older units: about 5 to 7 years

Many alarms manufactured in earlier years carried a rated sensor life of roughly five to seven years, after which the unit must be replaced. If you have an older First Alert CO alarm with a replaceable 9V battery and no printed replace-by date, assume the shorter end of that range and check the date of manufacture rather than guessing.

Current sealed 10-year units

Most current alarms are sealed 10-year units in which the sensor and a non-replaceable lithium battery are engineered to last a full decade. A sealed-battery model such as the one covered in our Kidde C3010 10-year sealed CO alarm review runs for ten years and then signals end of life. The trade-off is no battery swaps for a decade, followed by replacing the whole unit before the printed deadline.

The clock starts at manufacture, not installation

Critically, the service life counts from the date the alarm was manufactured, not the day you took it out of the box. A unit that sat in a warehouse or on a shelf for a year reaches expiration a year sooner than its install date would suggest. Always check the manufacture date when you buy, and prefer recently dated stock.

Part 3 — How to find the date code and replace-by date

Every UL-listed carbon monoxide alarm is marked with a date of manufacture, and many also print an explicit replace-by date. Knowing where to look turns the expiration question into a 30-second check.

Reading the back of the unit

Take the alarm off the wall or ceiling and look at the label on the back. You will find a date of manufacture, and on most current units a separate "replace by" date. If only a manufacture date is shown, add the manufacturer's rated life (commonly 7 or 10 years) to find the replacement deadline. A digital-display model like the First Alert CO410 with digital PPM display still carries the same printed date code on the housing.

What the end-of-life signal sounds like

When the sensor reaches end of life, a current UL 2034 alarm produces a distinct chirp or beep pattern that differs from the low-battery chirp, and digital units may show an "End" or "Err" code on the display. This signal means replace the alarm — not change the battery. If you are unsure which signal you are hearing, our guide on how to test a smoke and CO alarm walks through distinguishing the patterns.

Source: UL 2034 end-of-life signaling and CPSC / NFPA 72 guidance. The end-of-life pattern means replace the alarm, not the battery.

Part 4 — UL 2034, CPSC, and NFPA 72: the standards behind expiration

The expiration rule is not a marketing convention; it traces to the safety standard the alarm is built to and the codes that govern where it is installed.

UL 2034 and the end-of-life warning

UL 2034 is the U.S. safety standard for single- and multiple-station carbon monoxide alarms. Current editions require an end-of-life warning so that a homeowner is alerted when sensor life is exhausted, rather than left with a silently failed unit. A UL listing on the package is your confirmation the alarm meets this requirement; every alarm and carbon monoxide gas monitor we stock is UL 2034 listed.

CPSC guidance and NFPA 72

The CPSC carbon monoxide information center advises consumers to install CO alarms, follow the manufacturer's replacement schedule, and never ignore an alarm. CO alarm provisions formerly lived in NFPA 720; that standard has been withdrawn and carbon monoxide requirements are now consolidated into NFPA 72, National Fire Alarm and Signaling Code, which addresses placement and signaling. Local codes increasingly reference these requirements for homes with fuel-burning appliances or attached garages.

Part 5 — Placement and standard vs. low-level alarms

Expiration is only one half of effective coverage; where the alarm is mounted and what threshold it responds to determine whether it protects you in time.

On every level and near sleeping areas

CPSC and NFPA guidance call for a CO alarm on every level of the home and near each separate sleeping area so an alarm can wake occupants at night. A wireless interconnect unit such as the First Alert CO511 interconnect alarm sounds all linked alarms together. For full mounting rules — heights, distances from appliances, and what to avoid — see the CO detector placement guide.

Standard residential vs. low-level alarms

Standard UL 2034 residential alarms are designed to ignore brief, low concentrations and sound at levels and exposure times set to protect healthy occupants, which prevents nuisance alarms. Low-level CO monitors sound at lower concentrations and suit people who want earlier warning, such as those with heart or respiratory conditions. Either way, both types still expire on the sensor's schedule — a longer-lived sensor does not exist for the low-level category.

Part 6 — Combination smoke/CO alarms and smart units

Many homeowners run combination and connected alarms, and the expiration rule applies to them in the same way — with one wrinkle worth understanding.

Combination smoke and CO alarms

A combination smoke and CO alarm packs two sensors into one housing, and the unit expires when the shorter-lived sensor does. Because the whole device is replaced together, combination units are convenient but tie smoke and CO replacement to a single date. Check the label the same way you would on a standalone CO unit.

Smart and interconnected units

A smart CO alarm can push an end-of-life or low-battery notice to your phone, which removes the guesswork of identifying chirps by ear. The sensor still expires on schedule; the smart features simply make the warning harder to miss. Connected and hardwired models like the First Alert SMCO600NV hardwired smart smoke and CO alarm still print a manufacture date and must be replaced at end of life.

Part 7 — Worked example: checking the date code and deciding to replace

Here is the exact process a homeowner can use to decide whether a carbon monoxide detector has expired, using units stocked on this site as the replacement path:

1. Take the alarm down and find the date label. Remove the unit from the wall or ceiling and read the label on the back. Locate the date of manufacture and, if present, the separate "replace by" date. Note whether it is a replaceable-battery unit or a sealed 10-year unit.
2. Calculate the expiration from the manufacture date. If a replace-by date is printed, use it. If only a manufacture date is shown, add the rated life — about 5 to 7 years for older units, 10 years for current sealed models. Remember the clock runs from manufacture, so a unit installed a year after it was made expires a year earlier than you might expect.
3. Listen for and identify the end-of-life signal. A distinct chirp pattern, or an "End"/"Err" code on a digital model such as the First Alert CO615 plug-in alarm with digital display, confirms end of life. This is different from the slow single low-battery chirp — if a fresh battery does not stop the chirp, treat it as end of life.
4. Decide: replace the whole unit if expired or signaling end of life. If the unit is past its replace-by date or sounding end of life, replace the entire alarm — do not just change the battery. A sealed 10-year unit like the First Alert CO710 resets the replacement clock for a decade. For a simple plug-in replacement, the First Alert CO600 plug-in CO alarm is a straightforward swap.
5. Reinstall on every level and near sleeping areas. Mount the new alarm following placement guidance — one on each level and near each sleeping area. Write the install date on the housing with a marker so the next check is even faster.
6. Set a reminder for the next replacement. Record the replace-by date in your phone or on the unit. For whole-house planning and model picks, compare options in our best carbon monoxide detector guide.

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The same date-code check applies to every alarm in the house. Start from the home safety range and the Kidde CO alarm selection to replace any unit that is expired or nearing end of life.

Frequently asked questions

Do carbon monoxide detectors expire?

Yes. Carbon monoxide detectors expire because their electrochemical sensor has a finite working life and degrades over time, even if the alarm has never sounded. You replace the entire unit on the manufacturer's schedule — roughly 5 to 7 years for older models and 10 years for current sealed units. Browse current CO alarms when yours is due.

How often should I replace my carbon monoxide detector?

Replace it on the schedule printed on the unit: about every 5 to 7 years for older replaceable-battery alarms, and at 10 years for sealed 10-year models. The date is measured from manufacture, not installation, so check the back label. When in doubt, replacing on the shorter interval is the safer choice.

How do I know if my CO detector is expired?

Take the alarm off the wall and read the label on the back for a date of manufacture and any "replace by" date. If it is past that date, replace it. A distinct end-of-life chirp pattern or an "End"/"Err" code on a digital unit also signals expiration. Our testing guide helps confirm the signal.

What is the end-of-life chirp on a CO alarm?

It is a distinct chirp or beep pattern, different from the slow single low-battery chirp, that tells you the sensor has reached end of life. Many digital models also show an "End" or "Err" code. This signal means replace the whole alarm, not just the battery. UL 2034 requires current alarms to provide this warning.

Does the expiration start at manufacture or installation?

At manufacture. The rated sensor life counts from the date the alarm was built, which is printed on the back, not from the day you installed it. A unit that sat on a shelf for a year reaches end of life a year sooner than its install date suggests, so check the date code before you buy and prefer recently dated stock.

Can I just replace the battery instead of the whole CO detector?

Only for a genuine low-battery chirp on a replaceable-battery unit. If the alarm is signaling end of life or is past its replace-by date, a new battery will not restore the sensor — you must replace the entire alarm. Sealed 10-year units have no user-replaceable battery and are discarded whole at expiration.

How long does a sealed 10-year CO alarm last?

Ten years from its date of manufacture. The sensor and the non-replaceable lithium battery are both engineered to last a decade, after which the unit signals end of life and is replaced as a whole. Sealed units like the First Alert CO710 remove battery swaps for the full ten years.

Why is my carbon monoxide detector beeping if it isn't expired?

A slow single chirp every 30 to 60 seconds usually means a low battery on a replaceable-battery unit. A loud continuous four-beep pattern means CO is actually detected — get everyone to fresh air and call 911. A distinct chirp pattern that a new battery does not stop indicates end of life. Match the pattern to the cause before deciding.

What standard governs carbon monoxide alarms?

UL 2034, the Standard for Single and Multiple Station Carbon Monoxide Alarms, is the U.S. safety standard, and current editions require an end-of-life warning. Placement and signaling requirements that once lived in NFPA 720 are now in NFPA 72. Look for a UL 2034 listing on every CO detector you buy.

Where should I install carbon monoxide detectors?

Install a CO alarm on every level of the home and near each separate sleeping area so it can wake occupants at night. Follow the manufacturer's height and clearance instructions and keep alarms away from dead-air spots. The CO detector placement guide covers the full mounting rules.

What is the difference between a standard and a low-level CO alarm?

Standard UL 2034 residential alarms ignore brief, low concentrations and sound at thresholds set to protect healthy occupants, which limits nuisance alarms. Low-level monitors sound at lower concentrations for earlier warning, useful for people with heart or respiratory conditions. Both still expire on the sensor's schedule and must be replaced on time.

Do combination smoke and CO alarms expire too?

Yes. A combination smoke and CO alarm expires when its shorter-lived sensor reaches end of life, and the whole device is replaced together. Check the label for the date code exactly as you would on a standalone CO unit, and replace at the printed deadline.

Are smart CO alarms still subject to expiration?

Yes. A smart CO alarm can send an end-of-life or low-battery alert to your phone, but the electrochemical sensor still expires on its rated schedule. The smart features make the warning harder to miss; they do not extend sensor life. Replace the unit at end of life like any other alarm.

What should I do when a CO alarm sounds a real alarm?

Treat a loud continuous alarm as a genuine carbon monoxide event: move everyone to fresh air outside immediately, call 911 or the fire department, and do not re-enter until responders say it is safe. Do not silence and ignore the alarm. After a confirmed event, have fuel-burning appliances inspected before resuming use.

Can an old CO detector still work past its expiration date?

It may still power on and run self-tests, but you cannot trust an expired sensor to detect dangerous CO reliably — which is the entire point of the alarm. An expired unit can read normal while failing to respond to real exposure. Replace it on schedule regardless of whether it still chirps when tested.

Where can I buy a replacement carbon monoxide detector?

You can replace an expired unit from our carbon monoxide alarms and detectors catalog, including battery, plug-in, and sealed 10-year models from Kidde and First Alert. Compare picks in the best carbon monoxide detector guide before you buy.

Further reading on this site

• Carbon monoxide alarms and detectors — the full CO alarm catalog across battery, plug-in, and sealed 10-year units.
• CO detectors — UL 2034 listed detectors for every level of the home.
• Combination smoke and CO alarms — two sensors in one housing, replaced on a single date.
• Best carbon monoxide detector (2026) — editor picks by power type, display, and 10-year sealed life.
• CO detector placement guide — where to mount alarms on every level and near sleeping areas.
• How to test a smoke and CO alarm — distinguish the test, low-battery, and end-of-life signals.
• First Alert CO710 10-year sealed CO alarm review — a hands-on look at a sealed 10-year replacement unit.
• Kidde C3010 10-year sealed CO alarm review — a sealed-battery alternative for a fresh 10-year cycle.