The hungriest market is the nation's 19,000 law enforcement agencies.
Customs and Border Patrol has nine Predator drones mostly in use on the U.S.-Mexico border, and plans to expand to 24 by 2016. Officials say the unmanned aircraft have helped in the seizure of more than 20 tons of illegal drugs and the arrest of 7,500 people since border patrols began six years ago.
Several police departments are experimenting with smaller drones to photograph crime scenes, aid searches and scan the ground ahead of SWAT teams. The Justice Department has four drones it loans to police agencies.
"We look at this as a low-cost alternative to buying a helicopter or fixed-wing plane," said Michael O'Shea, the department's aviation technology program manager. A small drone can cost less than $50,000, about the price of a patrol car with standard police gear.
Like other agencies, police departments must get FAA waivers and follow much the same rules as model airplane hobbyists: Drones must weigh less than 55 pounds, stay below an altitude of 400 feet, keep away from airports and always stay within sight of the operator. The restrictions are meant to prevent collisions with manned aircraft.
Even a small drone can be "a huge threat" to a larger plane, said Dale Wright, head of the National Air Traffic Controllers Association's safety and technology department. "If an airliner sucks it up in an engine, it's probably going to take the engine out," he said. "If it hits a small plane, it could bring it down."
Controllers want drone operators to be required to have instrument-rated pilot licenses — a step above a basic private pilot license. "We don't want the Microsoft pilot who has never really flown an airplane and doesn't know the rules of how to fly," Wright said.
Military drones designed for battlefields haven't had to meet the kind of rigorous safety standards required of commercial aircraft.
"If you are going to design these things to operate in the (civilian) airspace you need to start upping the ante," said Tom Haueter, director of the National Transportation Safety Board's aviation safety office. "It's one thing to operate down low. It's another thing to operate where other airplanes are, especially over populated areas."
Even with FAA restrictions, drones are proving useful in the field.
Deputies with the Mesa County Sheriff's Office in Colorado can launch a 2-pound Draganflyer X6 helicopter from the back of a patrol car. The drone's bird's-eye view cut the manpower needed for a search of a creek bed for a missing person from 10 people to two, said Ben Miller, who runs the drone program. The craft also enabled deputies to alert fire officials to a potential roof collapse in time for the evacuation of firefighters from the building, he said.
The drone could do more if it were not for the FAA's line-of-sight restriction, Miller said. "I don't think (the restriction) provides any extra safety," he said.
The Montgomery County Sheriff's Office, north of Houston, used a Department of Homeland Security grant to buy a $300,000, 50-pound ShadowHawk helicopter drone for its SWAT team. The drone has a high-powered video camera and an infrared camera that can spot a person's thermal image in the dark.
"Public-safety agencies are beginning to see this as an invaluable tool for them, just as the car was an improvement over the horse and the single-shot pistol was improved upon by the six-shooter," said Chief Deputy Randy McDaniel, who runs the Montgomery drone program.
The ShadowHawk can be equipped with a 40 mm grenade launcher and a 12-guage shotgun, according to its maker, Vanguard Defense Industries of Conroe, Texas. The company doesn't sell the armed version in the United States, although "we have had interest from law-enforcement entities for deployment of nonlethal munitions from the aircraft," Vanguard CEO Michael Buscher said.
The possibility of armed police drones someday patrolling the sky disturbs Terri Burke, executive director of the Texas chapter of the American Civil Liberties Union.