Drones have harassed airports and bedeviled local police. They have trespassed over nuclear plants and prisons. On the battlefield, they can kill. But aside from shooting down the devices, which may create further danger, there’s often not much anyone can do to stop drones when they pose a threat or wander where they’re not welcome. That’s beginning to change. Cheap and easily modified, unmanned aerial vehicles have become a part of daily life as well as a tool for governments and bad actors alike — used for intelligence gathering, surveillance, sabotage, terrorism and more. Concerns about their misuse have spurred a technological scramble for ways to stop the devices in midair. “An adversary can use an off-the-shelf drone they bought for $500 and find out what’s going on at U.S. nuclear weapons bases,” said Zachary Kallenborn, a London-based national security consultant and expert on drone warfare. “China, Russia, Iran: If they’re not doing it they’re stupid.” Military drones are already potent weapons of war, used to track enemy movements and deliver attacks. But they have become an increasing threat at home, too. And anti-drone systems now hold significant promise for airports, water treatment plants, military installations and public events targeted by drones in recent years. The rise in incidents involving unmanned aircraft — like the wave of sightings reported last year in New Jersey — has led to more research and investment into the most effective ways of countering drones, preferably while preventing injuries to those below. Finding ways to counter drones safely Some systems work by firing a projectile to destroy it. Others jam the radio frequencies used to control the drones, causing them to land in place or fly back to their origin. Another approach uses other drones to fire nets at the offending devices. All the techniques have their strengths and weaknesses. Jamming a drone is highly effective and relatively easy from a technical standpoint. But it’s a blunt tool — jamming not just the drone’s signal but other electromagnetic signals used by telephones, emergency responders, air traffic control and the internet. The most basic anti-drone measures are called kinetic defenses, which involve shooting a missile, bullet, net or other projectile at the device to destroy or disable it. Kinetic systems can be risky, however, by creating the threat that debris could fall on people or property or that a missile fired at unmanned aircraft could miss and hit civilians instead. In 2022, for instance, 12 people were injured in Saudi Arabia when they were hit by debris after authorities took down a drone launched by Houthi rebels near the Yemen border. Hacking into drones The Israeli firm D-Fend Solutions created a system it calls EnforceAir that allows the operator to hack into an adversarial drone and take over its controls. The equipment looks like a large computer router and can be set up on a tripod or a vehicle or carried in a backpack. Like other anti-drone systems, D-Fend’s product also detects any drones entering a predetermined area, allowing the operator to permit friendly devices to fly through while disabling others. In a demonstration of the technology in an empty athletic field in suburban Washington, the system quickly hijacked a drone operated by one of D-Fend’s technicians as it entered an area being monitored. “We detect the drone, we take control and we land it,” said Jeffrey Starr, the company’s chief marketing officer. […]