[Alias_Knagg]

You might want to have a look at this lot. They all have their own little angle on the matter, but there could be one there that would work for you:

https://www.movesense.com/showcase/

[kbre93]

Interesting, thanks for sharing. It's cool they do it as a platform, but I'm not sure what the benefit over using a Polar H10 would be, which are widely available, I guess it would be custom branding of the hardware