Shortly after Alan Frazier became a part-time deputy sheriff in Grand Forks, N.D., the police began looking into the possibility of buying some aircraft to boost their law enforcement capabilities. They wanted some help doing things like finding missing people or carrying out rescues in a region dotted by farmsteads threatened by flooding that wipes out access to roads.

Buying a turbine engine helicopter, however, would cost $25 million, a prohibitive price tag even with 11 law enforcement agencies – eight from North Dakota and three in western Minnesota – willing to share the cost.

So Mr. Frazier, also an assistant professor of aviation at the University of North Dakota (UND), began looking into unmanned aerial vehicles (UAVs) as a possible alternative.

But what appears, on one level, to be a sensible, practical, and affordable solution for local law enforcement – the price tag for a small UAV is about the cost of a tricked-out new police cruiser at $50,000 – has run smack into public concerns about yet another high-tech invasion of privacy and the popular image of drones as stealthy weapons used against terrorists.

Nonetheless, the technology's potential benefits in pursuing a raft of public safety measures at relatively low cost have enormous appeal for law enforcement agencies across the country, since President Obama signed a bill last year directing the Federal Aviation Administration (FAA) to further open US airspace to drones for both public and private use.

Even before that, the number of permits, known as certificates of authorization (COAs), that the FAA issued to organizations to fly UAVs more than doubled from 146 in 2009 to 313 in 2011. As of February 2013 there were 327 active COAs.

The bulk of these permits go to the US military for training, and the Pentagon expects their numbers to grow considerably in the years to come. According to a March 2011 Pentagon estimate, the Department of Defense will have 197 drones at 105 US bases by 2015.

The US Border Patrol has the country's largest fleet of UAVs for domestic surveillance, including nine Predator drones that patrol regions like the Rio Grande, searching for illegal immigrants and drug smugglers. Unlike the missile-firing Predators used by the Central Intelligence Agency to hunt Al Qaeda operatives and their allies, the domestic version of the aircraft – say, those used by the border patrol – is more typically equipped with night-vision technology and long-range cameras that can read license plates. Groups like the American Civil Liberties Union (ACLU) also complain that these drones have see-through imaging technology similar to those used in airports, as well as facial recognition software tied to federal databases.

The growth in drones is big business. Some 50 companies are developing roughly 150 systems, according to The Wall Street Journal, ranging from miniature flying mechanical bugs to "Battlestar Galactica"-type hovering unmanned airplanes. It's an industry expected to reach some $6 billion in US sales by 2016.

Those forecasts notwithstanding, neither the FAA nor the association of UAV operators says it knows how many nonmilitary drones are operating in the United States. The ACLU is seeking that information.

The growth in the development of UAVs by both private companies and the US government has not gone unnoticed, creating a backlash in some communities.

In Seattle last month, community members quashed their city's drone program before it even got started. The program was being considered for search-and-rescue operations and some criminal investigations, but was referred to by protesters as "flying government robots watching their every move."

Mayor Mike McGinn spoke with Police Chief John Diaz, "and we agreed that it was time to end the unmanned aerial vehicle program," the mayor wrote in a statement. The drones were returned to the manufacturer.

Just days earlier, Charlottesville, Va., had become the first city in the country to pass a "no-drone zone" resolution, putting in place a two-year moratorium on the use of drones within Charlottesville limits.

"The big concern for us is that they're going to be everywhere," says John Whitehead, an attorney and president of The Rutherford Institute, a civil liberties organization in Charlottesville, which launched a preemptive fight against drones before the city council.

The move followed an Obama administration memo justifying the use of drones overseas to kill US citizens suspected of taking part in terrorist activities. "The president says you can take out American citizens in foreign countries," Mr. Whitehead says. "Well, if you can do that, you can take out somebody here as well."

On March 6, Attorney General Eric Holder may have reinforced such fears in testimony before the Senate Judiciary Committee when he refused to rule out the use of armed drones on US soil in an emergency "to protect the homeland."

If it all has an air of hysteria about it – Mr. Holder said there are no plans for the domestic use of armed drones and called the scenario "entirely hypothetical" and unlikely – privacy groups point to California's Alameda County, where officials insisted they wanted drones for search-and-rescue missions. An internal memo that surfaced from the sheriff's department, however, noted the drones could be used for "investigative and tactical surveillance, intelligence gathering, suspicious persons, and large crowd-control disturbances." The county dropped its plans.

The first and only known use of a drone in the arrest of a US citizen occurred in December 2011 in North Dakota, when the Nelson County Sheriff's Department asked to borrow one of the US Customs and Border Protection UAVs. The drone provided a good view of the three sons of the owner of a 3,000-acre farm who were involved in a standoff with law enforcement officers. As a result, police were able to tell that the brothers were unarmed, allowing them to enter the farm and arrest the brothers without the confrontation turning into a shootout.

Whitehead imagines a day when drones equipped with sound cannons, which release painful high-decibel sound waves that cause crowds to disperse, could be dispatched by the government to political protests and used as well to "effectively stifle free speech."

The concern that such technologies can be misused to invade privacy and suppress free speech "is a legitimate fear," says UND's Frazier. "Anytime we increase the technological capabilities of the government there's a justifiable concern there. But I think these fears can be offset by the fact that the drones we're using have very limited capabilities."

Nevertheless, privacy concerns are what have prompted groups including the nonprofit Electronic Frontier Foundation (EFF) to use the Freedom of Information Act to obtain hundreds of documents from the FAA outlining who has been requesting to use drones in America's skies, and why.

Roughly 40 percent of the drone flight requests submitted to the FAA are from the US military. "They are flying drones pretty regularly – eight hours a day, five days a week – to train pilots so that they will be able to fly drones," says Jessica Lynch, a staff attorney for EFF.

These drones are equipped with infrared scanning capabilities and other surveillance gadgets. "Drones have quite a number of technologies on board, including thermal cameras and the ability to intercept communications," Ms. Lynch says. "If they are training pilots, they are training them in these surveillance tools."

FAA regulations stipulate that weaponized drones cannot fly in unrestricted US airspace. The agency also has specific parameters for law enforcement drones. Law enforcement groups, for example, must maintain visual contact with the drone at all times and must also fly at relatively low altitudes.

These are regulations with which the Grand Forks Sheriff's Department has become familiar in the three years since it began looking into using drones, first establishing an Unmanned Aerial Systems unit as part of the department and then applying for COAs to use the drones. The unit, which went fully operational Feb. 1, has conducted 250 simulated missions, but has yet to use a drone in an operation.

Certification tends to be a lengthy and arduous process, Frazier says, adding that there are also some parameters for usage that are meant to promote safety, but can make it tricky for law enforcement to do its jobs.

One provision, for example, is that the drones can fly only by day. Another early rule was that the police had to give 48 hours' notice if they were going to use the drones.

"It's tough to predict if there is going to be a fire tomorrow, or a bank robbery the day after tomorrow," he says. The department was able to convince the FAA to let it fly the drones on one-hour notice instead.

That said, Frazier understands the public's concerns about the use of drones. For that reason, Grand Forks established a 15-member committee – made up of one-third public safety officials, one-third UND faculty, and one-third community residents – to evaluate the use of drones and to troubleshoot questions and concerns of the public. Every law enforcement action involving the drones is to be reviewed by the committee.

Frazier told committee members that the department did not intend to ask for the ability to use the drones for covert surveillance. "We will not use them to, quote, spy on people," Frazier says. Even if that were the intention, he adds, "These small drones are not particularly robust platforms for covert surveillance. I think the public can't understand that my little UAV can only fly for 15 minutes, can't fly out of my line of sight, and can't fly in greater than 15-knot winds."

Out of concern that average citizens could be filmed by sensors on the aircraft, one of the committee's first acts was to instruct police to post road signs warning the public when UAVs are in use.

Yet some of the conversations EFF's Lynch has had with other law enforcement agencies haven't been as reassuring about privacy, she says. "We've talked to police about this, and they've said, 'Well, we're going to fly the drones in public airspace, and if you walk around in public you don't have an expectation of privacy in your movements.'

"While that might be true for a police officer following you down the street, I don't know if that applies when a drone can fly over and surveil everybody walking down that street for an extended period of time," Lynch says.

"You can make the case that drones are helping law enforcement better do their jobs for less [cost] and we should incorporate it," she adds. "As technology becomes cheaper and easier to use, it's tempting to use it all the time."

That is the fear of Texas state lawmaker Lance Gooden, who in February proposed some of the toughest anti-drone legislation in the country. It would prevent drone operators from collecting images, sounds, and smells – or hovering over any home – without permission.

"Two to four years from now, it'll be impossible to get legislation passed because every law enforcement agency will want drones," says Mr. Gooden. While the drone lobby is growing, it is not as powerful as it will become, he adds.

Currently, his bill has the support of 101 of the 150 members of the state Legislature. But some longtime drone experts say such laws are overkill and could impede growth of technology that is useful and relatively inexpensive.

"The ordinances that have been passed are absolutely absurd," says retired Lt. Gen. David Deptula, the first deputy chief of staff for Intelligence, Reconnaissance, and Surveillance for the US Air Force. "And what's precluded are the very valuable civilian applications in terms of traffic control, firefighting, disaster response, border security, the monitoring of power lines – the list goes on and on."

As for privacy concerns, "I can't think of another way of saying it, but that they are unfounded," Deptula adds. "All you have to do is look up in any major metropolitan city and see the cameras all around. And have they ever heard of satellites? Where do they think Google maps come from?"

Frazier concurs. People with a good zoom lens have better cameras than do his small drones, he adds, pointing out that one of the Grand Forks Sheriff's Department's drones has a simple off-the-shelf Panasonic.

The average GPS-enabled cellphone can now track people and their movements to within a few feet, he notes.

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That said, "I understand what people mean when they say it's 'creepy,' " Frazier says. "I value my privacy as much as anyone does – it's very sacred in this country." Even if they could do it legally, law enforcement agencies would be making a big mistake using drones for covert surveillance – for the time being, he adds.

"It would be a fatal mistake at this point. We really need to take a crawl, walk, run approach. To go to covert surveillance brings us to a run," Frazier says of the law enforcement community. "If that means we're not Buck Rogers in the 21st century, we're comfortable with that."