but if he hits somebody with his tonfa nobody can prove it
Proof of shock on a stick proves nothing - he could have been banging on a riot shield to intimidate.
2010 have been a lot of demonstration in germany and next to my already mentioned concept i had the idea that the sensor-stick could be part of a game for policemen in demonstrations. For every hit they get a point, they travel from demonstration to demonstration and can upload their rankings to the internet. there are then awards like " most hits in one battle", " overall winner" etc.