The Drone Defender directionally blocks GPS signals, on the assumption that the drone will land when it loses GPS (which is the case with 3DR and DJI products, but can be disabled)
From Popular Science:
The Battelle DroneDefender is a rifle made for electronic warfare, as first reported by Motherboard. The gun looks like a hodgepodge of science fiction props strapped together. Despite its appearance, it’s not made to fire any projectile. Instead, the DroneDefender works by jamming the communications of commercial drones, causing them to lose control and, ideally, land.
The DroneDefender s weighs less than 10 pounds and can be mounted on any existing weapon with a picatinny rail—a fairly standard mount found on military rifles.
The attachment jams GPS signals, as well as radio signals normally reserved for industrial, scientific, and medical radio communications (the ISM band). It’s primary targets are small commercial drones flown in places the federal government doesn’t want them to be: the radio bands it uses to disrupt drone signals are restricted, so this isn’t a product for everyday consumers annoyed by their neighbors quadcopter. Not to mention the fact that currently, the cost hasn't been publicized.