How to Read a Smoke Detector Date Code
· 2 min read
A smoke detector does not last the life of the house. It lasts about ten years from the day it was made. That day is printed on the back, and most people have never turned the unit over.
Where the date is
Twist the detector off its bracket. The label is on the back, sometimes on the side of the battery drawer. You are looking for a manufacture date or a line that says "replace by."
A plain date is easy: a month and a year, or a full day. Add ten years to a manufacture date. If the label already says replace by, that date is the end. You do not add anything.
If the same unit also detects carbon monoxide, read that date separately. A lot of CO sensors are done at seven years. The smoke side and the CO side do not share a birthday. The label is the authority.
What a code looks like
Some older units, including a lot of Firex alarms from the late 1990s, print a code instead of a sentence. In a Castle Rock house built in 2000, the unit on the ceiling was a Firex 120-538C. The code on the back was 97226. That is August 14, 1997. It expired in 2007. It was still installed.
If you can read a month and a year, use that. If the stamp is a code you cannot decode, or the ink is gone, treat the unit as expired. Guessing wrong leaves a detector that looks fine and does not work.
Homes built from 1995 to 2005
39% of Douglas County homes were built in that window. The original detectors in those houses were due for replacement years ago. A fresh battery does not reset the clock. The sensor ages whether the alarm is quiet or not.
No date, a date you cannot read, or a unit that was there when you bought the house a decade ago: replace it. On a visit we take one down, read the code, and write the date for every detector in the home.