The search for a missing Ellicott City man was stretching into a fifth day this summer. But when a volunteer launched his privately owned drone into the air over a densely wooded area of Columbia, a search party found the injured 44-year-old within minutes.

Howard County police say they envision more of those scenes unfolding in the future. Chief Lisa Myers announced plans earlier this month to launch a one-year “field test” of three drones, which she hopes can help officers find missing children and scope out dangerous situations.

The suburban police department is the latest police agency in Maryland to embrace the potential of drones as the small, buzzing aircraft — often equipped with cameras and sensors — become more affordable and easier to use. But the rapid growth of the unmanned aircraft in law enforcement has also prompted concerns from privacy and civil liberties advocates, who worry that police will shift to more intrusive uses as they expand their drone programs.

“With most surveillance technologies, we see that law enforcement . . . [will] say it’s for one thing, but as soon as they have it, they start expanding,” said Dave Maass, a senior investigative researcher at the watchdog group Electronic Frontier Foundation.

Nationwide, the number of public safety agencies using drones more than doubled between 2016 — when the Federal Aviation Administration finalized rules for non-recreational drones — and 2018, according to researchers at the Center for the Study of the Drone at Bard College in New York.

Departments in every state except Rhode Island now have them, the center says.

In Maryland, police are using the small unmanned aircraft to investigate crashes, photograph crime scenes and survey damage after severe weather. The Cecil County Sheriff’s Office said it used the technology in 2017 to locate nearly $400,000 worth of stolen construction equipment on a property in Elkton.

Maryland State Police began testing drones in July, with the crash team using four drones. A dozen troopers are certified to pilot them, and the department says it has been able reduce the time it takes to collect evidence at an accident scene by more than two hours, spokesman Greg Shipley said.

The State Fire Marshal’s Office, an agency of the state police that investigates fires and explosions, is also using drones for mapping and collecting information at scenes, Shipley said.

Anne Arundel County police and the sheriff’s office in Carroll County are among the other departments in the state that use drones.

Baltimore County Police and the Harford County Sheriff’s Office say they are not using drones. Baltimore City police do not have any but are considering them, spokesman Matt Jablow said.

In Howard County, the move to fly drones comes after the police department grounded its helicopter unit in a cost-cutting move, which officials say will save nearly $1.8 million over four years.

The new drones will cost about $38,000, the department said.

“We’re looking at starting in a very measured way,” Myers said, adding that a work group studied the issue for months and the department plans to follow guidelines issued by the American Civil Liberties Union.

“I think transparency is huge,” Myers said. “We want the public to know that we’re doing our due diligence in researching and using this technology. We want the public to know that it is not our intention to infringe upon their privacy rights.”

When her department announced its plans, it said it would use drones in emergency situations and when there are “grounds to believe that the drone will collect evidence relating to criminal activity.” It said it wouldn’t use them for “mass surveillance.” And it said it won’t retain images “unless there is reasonable suspicion that they contain evidence” of a crime or are relevant to an investigation or criminal trial. The agency hasn’t yet completed the internal policy that will govern their use.

The Howard department plans to post information on social media as it rolls out the drone program and will publish statistics on how it uses the technology, Myers said. She expects county police to begin using drones early next year.

Police departments across the country have faced questions from the public about their use of drones, said Dan Gettinger, founder and co-director of the center at Bard.

“Nationwide, there’s a recognition that public engagement on this issue is a requirement,” he said.

Government use of drones has also sparked concerns about national security risks. Last month, the U.S. Interior Department grounded drones in its fleet made in China and those with parts made there. More than 80 percent of public safety agencies studied by the Bard researchers have acquired drones made by Chinese manufacturer DJI, Gettinger said.

In public safety, early adopters of drone technology tended to be smaller, more rural agencies, Gettinger said. Drones can help them cover a lot of ground quickly, and flying them over open land is less complicated than in urban areas dense with people and buildings.

But more recently, the nation’s largest departments, including those in New York and Los Angeles, have also begun using them.

Given Baltimore’s history with surveillance methods — including a surveillance plane program that operated for months in 2016 without public disclosure — sharing information with the public is key, said Maass, of the Electronic Frontier Foundation.

“Whenever they’re introducing a new one in Maryland, they should be paying special attention to being transparent,” Maass said.

In Carroll County, Lt. Christopher Orwig said his team has sought to share details of its drone program with the public by visiting community events, such as local public safety expos, to answer people’s questions.

Since the department got the drones about two years ago, deputies there said they have used the drones most frequently to investigate crashes. In another instance, they turned to the technology last summer to survey damage to the Cascade Lake dam in Hampstead after heavy rains. They’ve been called out to help find missing people, but in all those cases the person was found by traditional methods first.

The agency’s policy specifies several other types of incidents in which drones can be considered, including barricade and hostage situations and tracking suspects fleeing from the scene of a crime. It says the drones will not be used to establish probable cause for a search warrant. Under the policy, they can’t be flown over crowds “except during emergency situations.”

The sheriff’s office used about $20,000 in federal Homeland Security grant money to cover initial costs, which included four drones, support equipment, licensing and training, Orwig said.

Anne Arundel County police have two drones, purchased about two years ago for $1,200 each with operating funds, spokeswoman Sgt. Jacklyn Davis said. The department uses one for fatal crash reconstruction and the other for “extraordinary tactical uses.” The agency declined to elaborate on the tactical deployments.

While Anne Arundel County also has a traditional aviation unit featuring helicopters, most police departments can’t afford to purchase and operate manned aircraft, said Don Shinnamon, a retired Baltimore County police colonel who now works in the drone industry. One helicopter can cost millions of dollars, he said.

Drones used in policing range from less than $2,000 to more than $20,000, depending on their battery life, camera quality and how they withstand wind and rain, said Shinnamon, who became a police chief in Florida after leaving Maryland and was the longtime chairman of the aviation committee of the International Association of Chiefs of Police.

“Having inexpensive, very capable systems available has allowed more agencies to explore the use of the technology,” Shinnamon said.

Shinnamon said police should consider publishing annual reports detailing how they use their drones.

“It’s best just to show people what you have and what you’re doing with it,” he said.

Maryland law does not require police to get a warrant to use a drone, though some lawmakers have unsuccessfully sought legislation to do so.

At least 18 states have passed laws to require police to obtain a warrant before using a drone for surveillance or searches, according to the National Conference of State Legislatures.

Del. Warren E. Miller (R-Howard), a co-sponsor of such past legislation in Maryland, said police use of drones raises “constitutional concerns,” such as the Fourth Amendment protection against unreasonable searches and seizures.

“There’s a balancing act that has to go on,” Miller said. “You have to be very careful when you implement technology.”

Jessica Anderson contributed to this report.