CHERNIHIV, Ukraine — On a cool evening last month, 12-year-old Anatolii Prokhorenko was up in a pear tree, cutting off a damaged branch for a neighbor, when he heard the buzz of a drone.

That sound often means death in Ukraine, and not just for soldiers on the front lines. Increasingly, civilians are tracked, chased and attacked by small, commercially available drones equipped with cameras, rigged with explosives and steered by fingers-on-joysticks a dozen miles away.