With up to 200km/h (125mp/h for you american folk) with regular trains and even more with our high speed trains!

I dont know how much information a SmartWatch can send to thier mother company without the proprietary app. But I’d suggest you use gadgetbridge to syc it to your phone.

https://f-droid.org/packages/nodomain.freeyourgadget.gadgetbridge/

It’s open source and I bet there’s some way to hook it up to your NAS.

*edit Be sure to check compatibility with your watch before buying they have a list here: https://gadgetbridge.org/