Late on the night of April 24, 2015, 19-year-old Brayan Valle stood in a farm field half a mile north of the Mexico border near Calexico, California. When a drone launched in Mexico buzzed out of the darkness, Valle used a radio controller to command the commercial-grade, multirotor aircraft to drop a seven-pound bundle enclosed in bubble wrap. As Valle collected the bundle, the drone flew back to Mexico.

In a process that took hours to complete, the Mexican drone returned three times to drop additional seven-pound bundles. With the fourth and final bundle stuffed inside a backpack, Valle walked up to Highway 98, where he flagged down his new friend, 18-year-old Jonathan Elias. Throwing the backpack into the trunk of Elias’ car, Valle hopped in the front seat and the pair drove off. Neither of them knew that U.S. Customs and Border Protection (CBP) agents had picked them up on a remote camera. When CBP agents stopped and searched their car, they found 28.55 pounds of heroin, worth nearly $1.5 million. Although the teens wound up in prison, the drone and its Mexico-side pilot made a clean getaway. Valle and Elias were convicted in the country’s first seizure of a narcodrone, an uncrewed vehicle transporting illegal drugs from Mexico to the United States.

The typical narcodrone is small and inexpensive, like the quadcopters available at Best Buy and Walmart for a few hundred dollars, but some unpiloted aerial smugglers are six- and eight-motor aircraft, like those used in Hollywood filmmaking, and can cost more than $5,000 and carry up to 35 pounds. Nobody knows how many narcodrones cross the border each day, and nobody knows how to stop them from coming.

Tim Bennett is the program manager for air domain awareness at the Department of Homeland Security’s Science and Technology Directorate. His job is devoted to detecting, tracking, and countering drones. Narcodrones, he says, are “a new big problem that we all have to address. It isn’t just DHS [Department of Homeland Security]. It’s across all agencies in our government and all governments in the world.”