"The complaint would've ended right away," he said.

Laurel police Chief Richard P. McLaughlin said he's seen a decline in complaints and use-of-force incidents — though he could not provide statistics. The videos have shown him a remarkable change in attitudes, he said.

"It was Jekyll-and-Hyde situation," McLaughlin said, recalling one incident. "[A man] was drunk, he was belligerent. He was just mouthing off to police." When police told him he was being recorded, the chief said, the man quickly became cooperative.

Waddell said police have also been getting a different reception at troublesome bars where the regulars are known to officers. Patrons once looked for a fight, he said, but they quickly comply with the instructions of camera-equipped officers.

Laurel's Police Department, which has about 70 officers, purchased an initial set of cameras in January for about $2,000 apiece — which includes the camera, storage and backup technology.

The camera footage could also prove useful for prosecutors.

"Anytime we can have use of technology to prove our case, we're going to be supportive of it. This will be another good tool," said John Erzen, a spokesman for the Prince George's County state's attorney's office, which handles cases from Laurel and Hyattsville — another department that has begun using cameras.

Erzen said the office has not yet used any video in trials.

Although video recordings can provide a valuable tool to law enforcement in criminal cases and protect agencies from unfounded lawsuits, some say it raises broader questions about police and public relations.

"There's a part of me that thinks this is a great idea," said Wexler, of the police research group. "But a part of me thinks: Has it really come to this? Just talking to a police officer you are being recorded. It strikes me as unfortunate, but maybe necessary."