Camera shutter of Bluetooth shooter button to start stop activity

As not everybody is running with the separate running watch, is hard to start-stop activity when the phone is in armband or in pocket, so I am suggesting to add feature to application that activity could be started by pressing any of physical buttons in phone (for example my sony Xperia has photo shutter separate button) or Bluetooth shutters from photo sticks.  Maybe even Bluetooth headphones could send this kind of signal.

Bluetooth shutters buttons are quite cheap and popular so will be easy to carry in hand and even use and then put in a pocket, as is physical button is easier to do without looking into a screen.