When I was working, some years ago now there was a company supported scheme to get us all to walk about more and get fitter! I bought a FitBit as the supplied pedometer was some what pants, this synced via my mobile phone. The FitBit worked well but the physical side it left a lot to be desired. The first ones I had where an all in one design and the straps gave out, slowly failing, the only good thing was the customer service, when it started to happen a quick chat on their web site and an upload of a picture and a new one was shipped out to me.
I went though 3 different types of FitBit and was very upset when they pushed a firmware update on to the last one and it would no-longer sync with my phone.
I now have a Garmin Vio Sport.
I wear it almost constantly, it has survived a number of mishaps and the only thing to break is the little loop that snuggles the end of the strap.
I tried to buy a replacement but the closest I could was not quite the same.
It was a bit bigger and did not have the little pip to help keep it in place.
So I tried to draw a replacement, I started in Fusion 360 and while I managed to draw a loop that looked right I could not get the loop and pip exported was on STL file. I had watched a few youtube videos and one used Tinker CAD. I tried that and while the loop is not quite the same I managed to produce an STL file.
Then the fun began I only had PLA filament and so tried printing with that here are the attempts.
Getting the pip to print required me to change some of the settings in the slicer. I ordered some TPU filament, that is some what flexible and printed one.
It came out well but when I tried it I found I had made the gap too wide, so back to Tinker CAD and reduce the dimension by 1 mm, re-slice and reprint.
And there it is keeping the end of the strap from getting caught on things.