Sadly I don't think these devices fit within SuperUser's scope.
As it is more an IoT device you might want to try Internet of Things. According to their help files
If you have a question about...
- controlling, automating and sensing the environment using electronics ('smart devices'),
...
... you're in the right place!
I would say that a FitBit is a smart device that senses it's environment. You might want to check on their meta first though.
