What open API fitness trackers can be used?

Question

API

Hello!
Maybe someone knows which fitness tracker has an open API, while it has a low cost. It is necessary to make sure that all the data that the fitness tracker receives is transferred to a specially written Android / iOS application, and then uploaded to the database, where it will already be distributed among people's accounts. The best one seemed to be Xiaomi MiBand, but unfortunately it was difficult to get data from it.
If you know such fitness trackers, or if there are any articles (I used Google) about getting all the data from MiBand, or if you are just interested in this topic, I can tell you more, I'm waiting for answers. Thank you all in advance.

Answer 1

https://github.com/pangliang/miband-sdk-android
What's so hard about getting data from MiBand?

Answer 2

MiBand can be linked to Google Fit, which probably has an API.