How Often Should Smoke and Carbon Monoxide Detectors Be Replaced?

Smoke and carbon monoxide detectors don't last forever, and unlike a leaky faucet, a failing detector gives you no obvious warning. The sensors inside them degrade slowly, so a unit can look and sound fine while quietly losing the ability to do its one important job.

Here's how long they're actually built to last, and what's worth keeping a record of so you're never guessing.

The short answer

• Smoke detectors: replace about every 10 years from the manufacture date.
• Carbon monoxide (CO) detectors: replace about every 5 to 7 years, depending on the model.
• Combination smoke/CO units: follow the shorter of the two — usually 7 to 10 years, but check the label.

These are the timelines major manufacturers and fire safety organizations point to. The clock starts at the date the unit was made, not the date you installed it — a detector that sat on a shelf for two years is two years closer to retirement.

Why detectors expire

It's easy to assume a detector is good as long as it powers on and the test button works. But the test button only confirms the alarm and battery are working — it does not test whether the sensor can still detect smoke or CO.

Smoke detectors

The sensing element (ionization or photoelectric) becomes less reliable over years of exposure to dust, humidity, and ordinary household air. After roughly a decade, the chance of a missed or false reading climbs enough that replacement is recommended rather than continued use.

CO detectors

CO sensors use a chemical or electrochemical element that simply wears out. Many newer units have a built-in end-of-life signal — a distinct chirp or a specific light pattern — that tells you the sensor is done, regardless of battery status. That sound is not a low battery; it means the whole unit needs replacing.

Find the date on yours

Most detectors have a manufacture date printed on the back, on the body, or inside the battery compartment. Take the unit down, look for the date, and count forward.

If there's no date and you have no record of when it was installed, treat that as a sign it's time to replace it. An undated detector of unknown age isn't doing you any favors.

What to keep a record of

This is exactly the kind of thing that's easy to lose track of across a whole house. A simple home record makes it effortless. For each detector, note:

• Location (e.g. upstairs hallway, kitchen, primary bedroom)
• Type (smoke, CO, or combination)
• Manufacture date and install date
• Replace-by date (manufacture date plus the unit's rated lifespan)
• Battery type and the last time you changed it

With those dates logged, you'll get ahead of replacements instead of reacting to a 3 a.m. chirp. It also helps when you're at the store deciding which units to buy — you'll know exactly how many and what kinds you need.

A few related timelines worth knowing

• Batteries: in units with replaceable batteries, swap them at least once a year. A common reminder is to do it when clocks change.
• Sealed 10-year units: some newer detectors come with a non-replaceable sealed battery designed to last the unit's full lifespan. When the battery dies, you replace the whole detector.
• Hardwired detectors: these are wired into your home's electrical system and usually have a backup battery. They still expire on the same ~10-year schedule.

When to call a professional

Replacing a plug-in or battery detector is straightforward for most homeowners. But hardwired and interconnected detectors — the kind where one alarm triggers all of them — are tied into your home's wiring. If yours are hardwired and you're not sure how they're connected, it's worth having a qualified electrician handle the swap so the interconnection keeps working as intended.

The goal isn't to do everything yourself. It's to know what you have, know when each piece ages out, and have that information ready when you or a pro need it.