The way an object moves in the sky can also reveal whether it's a drone or a plane, he said. Drones tend to hover, make abrupt directional changes, or move erratically, owing to their small size and agility. Manned aircraft follow smooth, linear flight paths, especially in controlled airspace, where their routes are more predictable.

The FBI says more than 5,000 drone sightings the bureau investigated in New Jersey ended up being small planes, hobbyist drones, helicopters, stars or law enforcement aircraft.