My wife bought me a new fitbit for Christmas (mine is getting old, frequently just loses it's charge, etc). It would not allow me to initialize it without syncing to my phone, which had to be running their app. I wound up returning it because I don't _want_ to run their app on my phone.
I even looked into if it might be possible to work around the issue. Turns out, the fitbit, which is advertised as having a GPS, actually uses your phone's GPS. It has one of it's own, but it's apparently absolute garbage; it's inaccurate and it drains the battery extremely fast.
I'm still using my barely functionalit fitbit charge 2.
Pine64 is working on a smart watch. If you are a developer it might be worth hacking on.
Just pointing this out for those in the same boat as you. Personally I hate things on my wrist and so I don't know if it is any good as I won't be using it anyway.
Unfortunately that's the price you pay to use most devices - they need accompanying proprietary software. There doesn't seem to be a big enough market for open-standard or open-protocol health/fitness tracking.
But... it doesn't. I can look down at my old, not-phone-connected fitbit any time I want and see how many steps I've walked so far during the day. Or what my heart rate it. Or any number of other things.
It doesn't _need_ the phone to be able to do that part of it's job. And I don't want the "challenge your friends to a walk-a-thon" junk that does use the app.
There is a semi-open standard and protocol for fitness tracking: the FIT file format and ANT+ for wireless networking. However most devices which support those standards like Garmin generally require the use of a proprietary mobile app for initial setup. Once you finish that you can uninstall the app.
I even looked into if it might be possible to work around the issue. Turns out, the fitbit, which is advertised as having a GPS, actually uses your phone's GPS. It has one of it's own, but it's apparently absolute garbage; it's inaccurate and it drains the battery extremely fast.
I'm still using my barely functionalit fitbit charge 2.