Before you begin. This procedure is general reference information, not professional advice. Equipment varies by manufacturer, model, and year. Always follow the documentation supplied with your equipment — where it differs from this page, follow the manufacturer. Verify that you have the tools, the working conditions, and the ability to do this task safely. If anything is unclear, if the equipment is damaged, or if the task exceeds your experience, stop and use a qualified professional. You are responsible for your own safety and for the outcome. This site accepts no liability for any loss, damage, or injury arising from the use of this information.
Specifications marked unverified could not be traced to a manufacturer source. Do not rely on them — obtain the value from your equipment documentation.
Summary
A smoke alarm can look perfectly healthy and still be past its working life, because the part that wears out is the sensor inside, not anything you can see or hear during a monthly test. The United States Fire Administration states a single, clear rule for this: replace the whole alarm ten years from its date of manufacture. That date is stamped on a label most people have never looked at, on the back of the alarm, and reading it means taking the alarm down for a minute. This page is only about that one task: finding the date, reading it correctly, and deciding whether the alarm has reached the end of its working life. It does not cover changing the battery or testing the alarm; that procedure, and the monthly test schedule, is a separate page. A carbon monoxide alarm looks similar on the wall but is a different device with a disputed service life, and this page does not cover it either.
What this page will not do is tell you how to read an encoded serial number, because a smoke alarm's manufacture date is normally printed in the open on the label rather than hidden inside a scheme a reader has to translate. Kidde's own support documentation states plainly that the manufacture date code is stamped on the label on the back of the alarm, not buried in a code only the manufacturer can decode. The one real complication is the alarm with a sealed, long-life battery: the United States Fire Administration's own maintenance guidance tells the owner of that type to replace the whole unit according to the instructions of the manufacturer, rather than giving the same flat ten-year figure it gives for the other two types, so this page names that difference instead of smoothing it away. A hardwired alarm is covered as far as reading the label; the National Fire Protection Association says a qualified contractor should do the replacement of a hardwired unit, so this page stops there. If the label is missing, damaged or unreadable, this page tells you to treat the alarm as unknown in age rather than assume it is safe.
Safety
DO NOT USE A CHAIR OR A TABLE TO REACH THE ALARM.
A chair or a table can move under your weight. You can fall and injure yourself. Use a stable step stool with a wide base.
Necessary equipment
| Item | Note |
|---|---|
| Stable step stool | The step stool must have a wide base. |
| Flashlight optional | The print on the back label is small. |
| Camera or phone | Use this to make a photograph of the back label. |
| Pen and paper | Use these to record the date of manufacture. |
Find the alarm
Estimated 2 min
- Put a step stool below the alarm.1mReport a problem with step 1, Find the alarm
- The step stool must be stable.
- The step stool must have a wide base.
- Do not use a chair or a table.
DO NOT PULL THE WIRE CONNECTOR OF A HARDWIRED ALARM.
Exposed wire ends behind the mounting plate can give you an electric shock.
- Remove the alarm from the mounting plate.<1mReport a problem with step 2, Find the alarm
- You turn most alarms to the left to remove them.
- Hold the alarm with one hand.
- If the alarm has wires, do not pull the wire connector.
- Point the flashlight at the back label from one side.<1mReport a problem with step 3, Find the alarm
- Light from one side lowers the reflection on the label.
- The print on the label is very small.
Read the date on the back label
Estimated 3 min to 6 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Read the date of manufacture from the back label.1mReport a problem with step 1, Read the date on the back label
- Kidde prints the date code on the label on the back of the alarm.
- The layout of the label is different for each manufacturer.
- A month and a year are enough to calculate the age of the alarm.
- Write the date of manufacture in your records.<1mReport a problem with step 2, Read the date on the back label
- Make a photograph of the full back label.<1mReport a problem with step 3, Read the date on the back label
- The photograph keeps the date after the label becomes hard to read.
- Include the model number in the photograph.
INSTALL THE ALARM ON THE MOUNTING PLATE IMMEDIATELY AFTER YOU READ THE LABEL.
The home has no protection from fire while the alarm is off the mounting plate.
- Install the alarm on the mounting plate again.<1mReport a problem with step 4, Read the date on the back label
- Turn the alarm clockwise until it stops.
- Make sure that the alarm is tight on the mounting plate.
Decide whether to replace the alarm
Estimated 3 min to 5 min
No tier-1 source was found for this value. Take it from the documentation supplied with your equipment.
- Calculate the age of the alarm from the date of manufacture.<1mReport a problem with step 1, Decide whether to replace the alarm
- Subtract the year of manufacture from the current year.
- Use the month of manufacture when the year alone is not clear enough.
REPLACE THE ALARM WHEN IT IS 10 YEARS OLD OR OLDER.
An aged sensor can fail to sense smoke, even with a new battery, and put the home at risk.
- If the alarm is 10 years old or older, replace the entire alarm.<1mReport a problem with step 2, Decide whether to replace the alarm
- Count the 10 years from the date of manufacture, not from the date of purchase.
- Treat an alarm with no readable date as 10 years old or older.
- If the alarm has a sealed long-life battery, follow the instructions of the manufacturer for the replacement age.1mReport a problem with step 3, Decide whether to replace the alarm
- The United States Fire Administration gives this instruction only for the long-life battery type.
- Find the instructions of the manufacturer in the box or on the website of the manufacturer.
- For a hardwired alarm, arrange the replacement with a qualified contractor.1mReport a problem with step 4, Decide whether to replace the alarm
- The National Fire Protection Association gives this instruction for a hardwired alarm.
- Do not remove the mounting plate of a hardwired alarm.
- A qualified electrician must do all work behind the mounting plate.
After the job
Estimated 2 min
- Keep the date, the photograph and the model number with your home records.<1mReport a problem with step 1, After the job
- Make a yearly reminder for a check of the age of each smoke alarm.<1mReport a problem with step 2, After the job
Terminology
This page uses one term for each item and holds it throughout, as ASD-STE100 requires. Equipment sellers and other guides use the names below for the same parts.
- smoke alarm
- Also called: smoke detector, fire alarm, fire detector, smoke sensor, ceiling smoke detector
- date of manufacture
- Also called: manufacture date, date code, born-on date, expiry date, expiration date, 10 year smoke alarm date, when was my smoke alarm made
- mounting plate
- Also called: mounting bracket, base plate, backplate, alarm base
- sealed long-life battery
- Also called: 10-year battery, 10-year lithium battery, sealed lithium battery, long-life lithium battery, tamper-resistant battery
- back label
- Also called: data label, rating label, serial number label, sticker on the back of the alarm, date on the back of a smoke alarm
When to use a professional
This page reads a label and calculates an age. It does not open the battery compartment. It does not do a test of the alarm.
Stop if you cannot reach the alarm from a stable step stool. Ask your local fire department for help. In many places, the fire department installs or examines a smoke alarm at no cost.
Stop if the alarm has wires. Do not remove the mounting plate. Do not pull the wire connector. A qualified electrician must do all work behind the mounting plate. Arrange the replacement of a hardwired alarm with a qualified contractor.
Read the instructions of the manufacturer of your alarm before you make a final decision about a replacement.
Common questions
How old is my smoke alarm?
Take the alarm off its mounting plate and look at the back: nearly every unit carries a printed date of manufacture on a label there, and the United States Fire Administration counts the required ten-year replacement from that date, not from the day you bought it or moved in. Kidde's own support pages describe the same thing for their alarms: the date code is stamped on the back label, in the open, not hidden inside a serial number you would need to decode. Write the date down and do the subtraction yourself; an alarm made in 2016 is already at the edge of its working life in 2026. If the label has gone blank or you cannot find a date at all, the safe assumption is that the alarm is old enough to replace.
Do smoke alarms expire?
Not the way food does, but yes, in the sense that matters: the sensor inside ages even if the alarm still passes its monthly test, and the United States Fire Administration says the whole unit needs replacing ten years from its date of manufacture. The National Fire Protection Association's own installation guide is blunt about it, stating that smoke alarms should be replaced when they are ten years old and that a new battery does not change that. An alarm that beeps happily on the test button can still be past the point where its sensor is reliable; the date on the back label is the figure that governs replacement, not how the alarm sounds today.
Where exactly is the date printed on the back of a smoke alarm?
On the label on the back of the unit, according to Kidde's own support documentation, which states that the manufacture date code is stamped on that label along with the model number. You have to take the alarm off its mounting plate to see it; on most alarms this means turning the unit counterclockwise until it comes free. The exact layout of the label is different for each manufacturer, so read yours directly rather than guessing from a description of someone else's alarm; a flashlight held to one side helps with the small print.
When should I replace a smoke detector?
As a rule, ten years after its date of manufacture, according to the United States Fire Administration, and that applies to a 9-volt battery alarm and to a hardwired alarm alike. The one exception the United States Fire Administration itself names is the alarm with a sealed, long-life battery: for that type it points you to the instructions of the manufacturer rather than giving the same flat figure. Replace an alarm sooner than ten years if it fails a test even after a fresh battery, or if the date on the back label is missing or unreadable.
What does '10-year smoke alarm' mean?
It usually means an alarm built with a sealed lithium battery meant to last as long as the alarm itself, so there is no battery door to open and no yearly battery change. It does not mean the alarm lasts longer than a battery-powered one before it needs replacing: the United States Fire Administration's ten-year replacement figure, counted from the date of manufacture, is the same figure that applies to the other alarm types. The 'ten year' in the name describes the battery, and the ten years in the replacement rule describes the whole unit; the two just happen to be the same number for this alarm type.
Is the ten-year rule the same for a carbon monoxide alarm?
No. A smoke alarm has a single figure behind it, from a federal agency, counted from the date of manufacture. A carbon monoxide alarm does not: its manufacturers and health and safety agencies publish different service-life figures for different models, and this site does not average them into one number. If you have a combination smoke and carbon monoxide alarm, or a separate CO alarm, its own page covers the disputed replacement figure and how to find it.
Related procedures
- How to read a tire sidewall and find out how old your tires are
- How to find and record the model and serial number of every appliance in the house
- How to change the battery in a smoke detector and test it
- Find which alarm is chirping and what the chirp means
- Where should I put smoke detectors, and how many do I need
- How old is my carbon monoxide detector and when do I replace it
- How old is my water heater and how do I read the serial number
- How do I decode the date code on my appliance and find out how old it is
Sources
Every specification on this page is traced to one of these sources. Tier 1 is a manufacturer document, a published standard, or a government safety authority. See Standards for the full tiering rule.
- Tier 1Smoke Alarms
- Tier 1How to Find the Date of Manufacture on an Alarm
- Tier 1When Should I Replace My Alarms?
- Tier 1How to Find the Model Number on Your Alarm
- Tier 1Planning & Implementing a Successful Smoke Alarm Installation Program
Revision history
Current version 1 · updated 2026-08-03 · next review due 2027-08-03
- v1 · 2026-08-03First draft. Scoped to finding and reading the date of manufacture and deciding on replacement, deliberately excluding the battery-replacement and monthly-test procedure that replace-smoke-alarm-battery already covers. The ten-year figure is verified against usfa-smoke-alarms. The sealed long-life battery type is flagged separately because USFA's own per-type maintenance table defers to the manufacturer's instructions for that type rather than repeating the flat ten-year figure. Hardwired replacement is routed to a qualified contractor per NFPA's installation guide. No step opens, tests or replaces the alarm; it reads a label and decides.
Corrections to this page are listed in the public corrections log. Reports that are credible and not yet verified are listed in the public errata register, and an open one renders above the step it concerns.
Comments and corrections
Found an error? A correction with a manufacturer source is applied and logged publicly. You can also write to corrections@fixchecklist.com.
Every step above carries its own report control, which tags the report with that step so a correction reaches the right place. For anything about the procedure as a whole — the order of the sections, a step that is missing, something that did not match your equipment — use this: report something about this whole procedure.