On Tuesday, the Air Force called for proposals to helm it make a very small drone that could sneak up on people, spray them with tracking “Dust” – or “smart dust” – and then watch from afar. From Wired: The solicitation floats the idea of dropping a “dust-like” cloud of electromagnetic signal-radiating taggants, either on top of the target or in his path so that he’ll walk into it. To do that, they’d need to either do some high-altitude “crop-dusting” of the target or launch a small munition that would blow out the taggant in mid-air when it was nearby.