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Replace smoke alarms 10 years after the manufacture date and replace carbon monoxide alarms on the schedule their manufacturer sets. Replace either one sooner if it fails a test or sounds its end-of-life signal. A fresh battery does not fix an alarm that has reached the end of its life.
The age rules
For smoke alarms the rule is plain. The U.S. Fire Administration says they need to be replaced 10 years from the manufacture date. The NFPA desk reference adds where to look: the date is on the outside or back of the alarm, and if there is no date, replace the alarm. The CPSC agrees on the number and says to replace a smoke alarm that is more than 10 years old.
CO alarms are less tidy. The CPSC carbon monoxide Q&A says alarms have a recommended replacement age that you get from the product literature or the manufacturer. NFPA says CO sensors have a limited life and tells you to replace the alarm according to the manufacturer’s instructions or when the end-of-life signal sounds. One manufacturer, Kidde, says its CO alarms last 7 or 10 years depending on the model. So two CO alarms bought on the same day can have different deadlines.
| Alarm | Replace when | Where that comes from |
|---|---|---|
| Smoke alarm | 10 years from the manufacture date, or sooner on an end-of-life warning | USFA, CPSC, NFPA |
| CO alarm | At the manufacturer’s recommended age, or when the end-of-life signal sounds | CPSC, NFPA, Kidde |
| Combination smoke and CO alarm | Per the manufacturer’s recommendation | NFPA |
| Any alarm that fails a test | Right away | NFPA |
A note on counting. NFPA counts smoke alarm age from the manufacture date. The First Alert manual for one combination model counts from installation instead and says to replace that alarm 10 years after installation. If you only know the install date, the manufacture date is earlier, so the true age of the alarm is higher than you think.
Low battery or end of life
A chirp can mean two different things, and the fixes differ. NFPA’s guidance for CO alarms says that if the low-battery signal sounds, you replace the batteries or replace the device. That is the easy case.
The end-of-life signal is the one that new batteries will not stop. Kidde describes it for its CO alarms as a quick beep every 30 seconds with a flashing red LED, and says replacing the batteries will not stop the chirping once the unit has reached the end of its useful life.
The patterns are not universal, and that is the practical lesson. The First Alert combination model in the manual above chirps once about every 45 seconds for a low battery and five times about every 45 seconds at end of life. The count of chirps, not just the presence of a chirp, tells you which problem you have. If you cannot read it off the alarm, look up the manual for the model number.
That manual also says the end-of-life chirp can be silenced for up to 2 days, and that you should not unplug the alarm or remove the batteries until you have a replacement. In other words, silencing buys a short window to shop, nothing more.
When a test fails, or passes too easily
CPSC recommends testing smoke and CO alarms monthly, and NFPA says to replace a CO alarm that fails to respond when tested. The same goes for smoke alarms, where NFPA says to replace any alarm that does not alert when tested. The First Alert manual asks for a weekly test of its combination unit, so the manual for your model may be stricter than the agency minimum.
A passing test is weaker evidence than it feels like. The CPSC Q&A says the test button checks whether the circuitry is working, not the accuracy of the sensor. That is why age and the end-of-life signal count as separate reasons to replace an alarm. An old alarm can pass the button test and still be past its service life.
Batteries run on a different clock
CPSC says to replace alarm batteries at least once each year, unless the alarm has sealed 10-year batteries. That is a separate task from replacing the alarm, and it is easy to confuse the two when a unit is old and chirping.
Sealed long-life batteries change the math. NFPA says alarms with non-replaceable long-life batteries are designed to last up to 10 years from the manufacture date, and when one gives an end-of-life warning you replace the entire alarm. There is no battery swap to attempt. For wired and plug-in units, CPSC says hardwired or plug-in CO alarms should have battery backup, so a unit on household power still has a battery that needs attention.
Choosing the replacement
For a CO alarm, CPSC says to install one that meets the current UL 2034 safety standard, and NFPA says to choose one listed by a nationally recognized testing laboratory. For smoke alarms, the USFA recommends both ionization and photoelectric alarms, or dual-sensor alarms with both sensors.
The new alarm goes where the placement rules say. That means every level, outside sleeping areas, and inside bedrooms for smoke alarms. CPSC also says to keep CO alarms out of kitchens and away from the top of fuel-burning appliances, heating vents and anywhere furniture or drapes can cover them. The USFA recommends interconnected smoke alarms so that when one sounds they all sound, which is easiest to set up while you are replacing several at once. Our DIY home security setup guide and the renter security tips cover the mounting side if you rent.
A ten-minute walk through the house
Take a flashlight and a step stool. Pull each smoke alarm off its bracket and read the manufacture date. Write the replacement year on a piece of masking tape stuck inside the battery door so the next check is easy. Do the same for CO alarms, but instead of a fixed number, look for the model’s stated lifespan on the back or in the manual. Anything with no readable date goes on the replacement list, which is NFPA’s own rule for smoke alarms.
Our take
Keep two clocks. The battery clock runs yearly, and the alarm clock runs to 10 years for smoke alarms and to the manufacturer’s figure for CO alarms. If a unit gives its end-of-life signal, the whole alarm goes, not just the battery. The one gap in the sources: only Kidde and one First Alert manual give CO or combination lifespans here, so your own model’s paperwork decides.
Common questions about replacing smoke and CO alarms
Can I just change the battery when my CO alarm chirps?
Only if the chirp is the low-battery signal. Kidde says a CO alarm at the end of its life keeps chirping after new batteries go in. Check the manual for the chirp pattern of your model.
How do I find the age of a smoke alarm?
NFPA says the manufacture date is on the outside or back of the alarm. If there is no date, replace the alarm.
Do plug-in and hardwired CO alarms expire too?
Yes. CPSC says alarms have a recommended replacement age, and NFPA says CO sensors have a limited life. CPSC also says hardwired and plug-in CO alarms should have battery backup.
How long do CO alarms last?
It varies by model. Kidde says its CO alarms last 7 or 10 years, and the First Alert combination manual says to replace its alarm 10 years after installation. The product literature has your figure.
What if my alarm passes the test button check?
A pass means the circuitry works, according to CPSC, not that the sensor is accurate. Age and the end-of-life signal still apply.
Who checked this
True Security Gear does not run a test lab and does not take units apart. One half of the work is documents: manufacturer specs, certifications, and seller claims checked against the paperwork. The other half is the record owners leave behind, in verified-buyer reviews, owner forums, and warranty complaints. Where that evidence is thin we say it is thin, rather than filling the gap with an adjective. The criteria are on How we evaluate.
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