This was a super noisy, busy stand at Automechanika Frankfurt 2016 (I'm making excuses for the audio here) . Mirka aren't the first to market with this sort of monitoring system, but this looks like a good one.
Who cares how long you've been sanding? Well in Europe workshop managers care very much indeed as they can be sued if anyone under their management develops injuries though use/overuse of workshop equipment.
If you're not worried about being sued the app will also tell you when you are applying too much pressure.