Caltrops are an ancient weapon, targeted at the sole of mobility: the feet of any human or creature unfortunate enough to stumble across these erect spikes. Simple to manufacture and cheap to deploy in great quantities, these multi-pronged nails come with a handful of major limitations: they take effort to remove from the path after-the-fact, and it’s hard to distribute them effectively without injury. Dropping caltrops by drone does nothing for the first problem, but is one surefire answer to the second.

Spotted at a technology exposition in China, this hexacopter dropping caltrops suggests a range of possible roles for the technology in the future. In the simplest cases, it’s a low-cost aerial denial strategy, blocking uninhibited passage through an area without armor. In more advanced cases, the drone could block alleyways and streets, spiking tires in car chases and putting obstacles in paths difficult for pursuers on foot or wheels to reach.

Drone-dropped caltrops fall into the uneasy space where internal security tools and military tools overlap. The ways that caltrops deny movement in combat are exacerbated when the target in question is civilian protesters, and while the rules for setting up lines of fire may be more about tear gas than grenades in repression, the principles of how to employ such tech is largely the same.

An enduring feature of drones like this is how they work as utility players for distributing new and novel payloads. The caltrops stand alone as a fascinating fusion of ancient and modern technology, but it’s hardly the only payload that turns a hexacopter into a surprise weapon. On display at the same show was a similar hexacopter, outfitted with a submachine gun.