I have some 20 y/o hard-wired smoke detectors that I want to replace
with newer hard-wired ones. How do I figure out which circuit breaker to
trip or is this an issue with smoke detectors?

--
To find that place where the rats don't race
and the phones don't ring at all.
If once, you've slept on an island.
Scott Kirby "If once you've slept on an island"