I have a bunch of mechanical watches that are varying degrees of inaccurate by their nature, but I do have one that isn’t inaccurate at all. A square Gshock that uses six band radio towers to update itself nightly. Just as accurate as a phone, and I use it as my reference to set my mechanical watches.

So there’s at least that alternative. Silly I know, because I’ve always got my phone close by, but I just think they’re neat.