Tech Scout is a gear perk that tags extra enemies when you kill someone with a gadget. It rewards using throwables and mines, since each kill also reveals more targets.
A kill with a gadget, like a grenade or mine, marks more enemies nearby. You see the rest of the group without scanning.
Wear the Breach & Clear Headset or Techmaster Cap. Gear perks are fixed to the piece of clothing that carries them, so you get this one by wearing that piece, not by unlocking it in a menu.
Techmaster Pocket and Remote Gadget Pocket let you carry more gadgets to trigger it.