The Concussion Detonator is one of Batman's gadgets in Batman: Arkham Origins
If you use that instead of your fist, you'll do less lasting damage to those police officers and civil servants
Batman can attach this enemies and when it explodes it stuns and disorients any victim caught in the explosion
You unlock the Concussion Detonator as you progress through the game. Alfred will radio you to let you know it's ready, at which point you can use the Batwing to head over to the Batcave and pick up the Concussion Detonator from your Workbench