Smoke alarms: 10 years from manufacture. CO alarms: per the label, usually 5–10 years. How to find the date, read a chirp, and check your state's rules.
Key takeaways
- Replace smoke alarms 10 years from the manufacture date printed on the back—not the install date.
- CO alarms have no single national interval; check the label, commonly 5–10 years by sensor type.
- Testing monthly and replacing on schedule are two separate habits—one does not cover the other.
- A chirp every 30–60 seconds usually means low battery or end of life; a new battery never fixes end-of-life chirping.
- Install alarms on every level, outside each sleeping area, and inside every bedroom per NFPA.
- No single national smoke-alarm law exists—requirements vary by state and local code. Check yours before assuming.
Replace smoke alarms 10 years from the manufacture date, not the install date. NFPA says to test smoke alarms monthly and replace the entire unit at 10 years. USFA states it plainly: “Age matters when it comes to smoke alarms. They need to be replaced 10 years from the manufacture date.” CO alarms are different—there is no single national number. Check the label on your unit; sensor life commonly runs 5 to 10 years depending on the manufacturer and sensor type. The master checklist, spring checklist, and fall checklist each mention alarm testing as one line item—this page covers the dates, the chirps, and the law question those pages skip.
Smoke alarm vs. CO alarm replacement schedule
| Alarm type | Replace | Source |
|---|---|---|
| Smoke alarm (any battery type) | 10 years from the manufacture date | NFPA, USFA |
| CO alarm | Per the manufacturer’s label, commonly 5–10 years | CPSC carbon monoxide fact sheet says to follow the printed replacement age; CO sensors typically run shorter than smoke sensors |
| Combination smoke/CO alarm | Replace at the earlier of the two dates | The CO sensor usually degrades first; check both dates on the label |
| Sealed 10-year lithium smoke alarm | Still 10 years—the sealed battery does not extend sensor life | Kidde and other manufacturers confirm the whole unit expires with the battery |
There is no universal CO number because sensor chemistry and manufacturer testing differ. Check your unit’s label rather than assuming a single figure.
Find the actual manufacture date
Twist the alarm off its mounting bracket (most turn counterclockwise) and look at the back or side of the plastic housing. You’ll find a printed or embossed date, usually a month and year, next to a model number and UL listing mark. An “installed” date a previous owner or inspector wrote on a label is not the number that matters—the manufacture date is.
If you can’t find a date at all, treat the alarm as due for replacement. A missing date is also an alarm you can’t verify against the 10-year window.
Testing monthly and replacing on schedule are two different habits
These get conflated constantly, and they protect against different failures.
| Habit | What it catches | How often |
|---|---|---|
| Monthly test (press the button) | Dead battery, wiring fault, unresponsive unit right now | Every month—NFPA |
| Scheduled replacement | Sensor degradation from age, dust, and years of exposure that a working test button can’t detect | 10 years for smoke; per label for CO |
A smoke alarm can pass its monthly test and still be past its sensing life. The test button checks the electronics and horn—it does not measure whether the sensing chamber has degraded from years of dust, cooking residue, and humidity. That’s why the 10-year rule exists independently of a passing test.
Battery types: what the sealed 10-year unit actually changed
Older smoke alarms use a replaceable 9-volt battery, swapped once a year or whenever it chirps low. Newer units increasingly ship with a sealed, non-replaceable 10-year lithium battery built to last the alarm’s expected working life. That removes one failure mode—a dead 9-volt battery nobody replaced—but it does not extend the sensor’s expiration. When a sealed unit reaches end of life, the whole alarm gets replaced, because the sensor hit the same 10-year limit as the battery. Hardwired alarms with battery backup follow the same 10-year sensor rule; only the backup battery, usually replaceable, gets swapped annually in the meantime.
Decoding a chirp: low battery, end of life, or malfunction
Chirp patterns are not standardized across manufacturers, so treat this table as a starting point and confirm against your specific model’s manual.
| Pattern | Likely meaning | What to do |
|---|---|---|
| Single chirp roughly every 30–60 seconds, no other change | Low battery (replaceable-battery units) | Replace the battery, then test |
| Single chirp every 30 seconds that continues after a fresh battery | End of life or sensor fault (Kidde: “an end-of-life alert or sensor error will not respond to a battery change”) | Replace the whole alarm |
| Loud, repeating 3-beep pattern | Smoke or fire detected—an active alarm, not a chirp | Evacuate; this is not a maintenance signal |
| Multiple short chirps in a distinct pattern from the low-battery chirp | Manufacturer-specific fault code (varies by brand) | Check your model’s manual; First Alert directs owners to their unit’s manual for exact counts |
How many, and where: placement per NFPA
Replacement only matters if the alarms are in the right places. NFPA and USFA specify the same baseline:
| Location | Requirement |
|---|---|
| Every level of the home | At least one smoke alarm, including the basement |
| Inside every bedroom | One smoke alarm |
| Outside each separate sleeping area | One smoke alarm in the hallway or common area near bedrooms |
| Interconnection (where possible) | All alarms sound together when one activates—required in most new construction |
| CO alarms | On every level and outside sleeping areas; required near fuel-burning appliances or attached garages in many jurisdictions |
Mount alarms on the ceiling or high on a wall, away from kitchens and bathrooms where steam or cooking smoke triggers false alarms. Use a photoelectric unit or a hush feature near cooking areas instead of removing the alarm.
The “law” question, answered honestly
No single federal statute mandates smoke alarms in every existing home nationwide. What exists instead is a patchwork: state and local fire and building codes, many referencing NFPA 72 as the technical standard, that set requirements for new construction, rentals, and sometimes existing owner-occupied homes. Those codes vary on whether alarms must be hardwired, interconnected, or allowed to run on a sealed 10-year battery, and how soon existing homes must comply when a code updates. Some states now specify sealed 10-year batteries for battery-only alarms; others leave more discretion to local jurisdictions.
Don’t assume a rule applies to your house based on a blog post or a neighbor’s description of their state’s code. Check your state fire marshal’s office or local building department—especially if you’re selling, since many states require working, code-compliant alarms as a condition of sale.
Climate and household caveats
| Situation | What changes |
|---|---|
| Kitchens and bathrooms | False alarms from steam or smoke are common—use a photoelectric unit or a hush button, don’t disable the alarm |
| Attached garage or any fuel-burning appliance | Install a CO alarm nearby regardless of your state’s minimum |
| Rental or newly purchased home | Check both alarm dates immediately—you can’t verify a previous owner’s or landlord’s maintenance history |
| High-dust or high-humidity homes (near construction, coastal humidity) | Sensors can degrade faster than the rated life; treat chirping as urgent, not annoying |
When to call a professional
| Situation | Why it is not DIY |
|---|---|
| Hardwired or interconnected alarm system needs rewiring, adding a zone, or troubleshooting a wiring fault | Line-voltage work at the alarm and panel—licensed electrician territory |
| An interconnected alarm won’t sync with the rest of the system after a straightforward battery or unit swap | Could indicate a wiring or control-module fault, not a simple part swap |
| You smell gas or a CO alarm sounds | Leave the house immediately and call 911 or your gas utility—this is not a maintenance call |
| Code compliance for a sale, rental, or renovation is unclear | An electrician or your local fire marshal’s office can confirm what your specific code requires |
Related guides
Frequently asked questions
How do I find the manufacture date on a smoke alarm?
Take the alarm off its mounting bracket and look at the back or side of the unit. The manufacture date is printed or stamped directly on the plastic housing, usually as a month and year. It is not the same as the date you or a previous owner installed it.
Do CO alarms expire on the same 10-year schedule as smoke alarms?
No. There is no single national interval for CO alarms. Manufacturers rate CO sensors differently, commonly 5 to 10 years, and print the specific replacement date or interval on the unit’s label. Check your label instead of assuming 10 years.
What does it mean when my smoke alarm chirps every 30 seconds?
A single chirp roughly every 30 to 60 seconds usually signals a low battery or, on sealed 10-year units, an end-of-life warning—the interval varies by manufacturer, so check your model’s manual. A fresh battery clears a low-battery chirp; it will not stop an end-of-life or malfunction chirp, which means the whole alarm needs replacing.
Is there a federal law requiring smoke alarms in every home?
No single federal law sets one national smoke-alarm requirement for existing homes. Requirements come from state and local fire and building codes, which vary on interconnection, hardwiring, and sealed 10-year batteries. Check your state fire marshal or local code before assuming a specific rule applies to your house.
Can I just replace the battery instead of the whole alarm?
Only if the chirp is a genuine low-battery warning on a replaceable-battery unit. If the alarm is at or past its 10-year manufacture date, or a sealed 10-year unit is chirping at end of life, no battery swap fixes it—the sensor itself has degraded and the entire alarm needs replacing.