A wise man once said "don't turn it on, take it apart". Another one once said "if ain't broke, don't try to fix it...". I prefer "if it ain't broke, fix it until it is".
This is the place where dead tech gets operated on with all the skill and understanding of a Victorian barber-surgeon. Sometimes it survives, sometimes it doesn't. Either way I learn something new.
The Fitbit is waterproof, but it seems hot sweat can work its way in and short things out.