Well here is Dr Prakash’s answer (screenshot from his message) it says 1. As I asked several questions.

I had done my own research and found that there are several wearable products but they don’t mention movement or while exercising, Body movement is the main challenge. I’ve heard of people carrying a wrist device stopping and taking a measurement but wrist devices are not notoriously accurate.

If a wearable comes out that is decently accurate it will probably be easier to carry around, stopping and taking a quick measurement.