trader_4 wrote in
:

On Thursday, July 30, 2020 at 1:43:19 PM UTC-4, Mercellus Bohren
wrote:
do they ever need to be completely replaced?

That would depend on what it actually is. Smoke detectors are
supposed to be replaced at least every ten years. Some of the new
ones have a lifetime battery in them now.


The reason for replacing the whole detecter every so many years is that
most, if not all, can get dirty and become less efficient at detecting
smoke and other particles over time.