Jeff Guay wrote:
Hi,
My house has hard-wired 120v smoke detectors. One went off today for
a few seconds. So I climbed up to take a look, and I noticed on the
plastic housing it says replace by year 2005. I tried the test
button and it worked, I actually tried the test button on all the
detectors and they all worked. Should I replace all the detectors? They
seem to be working, based on the test button. I know there are
recommendations on replacing battery operated ones but not hard-wired
ones.

The "Test" button tests whether the sucker can make a noise, not whether it
can detect smoke. (Unless, of course, pushing the "test" button on your
device generates smoke not connected with electing a new Pope.)

The radioisotope may have decayed thereby exceeding its half-life by the
"best if used by" date. You may just need fresher radioactive material -
which means a new detector.