Police officers at the Springfield-Branson National Airport noticed a sharp decline in complaints after they started wearing body cameras. (Photo provided by Kent Boyd.)

Six years ago, police officers at the sleepy Springfield-Branson National Airport in Missouri started wearing what some Americans now demand to curb police brutality: body cameras.

About the size of a pack of gum, they perch on the officers’ chests. They cost about $110. They capture mostly parking tickets.

But the so-called “bodycams” may offer lessons for mending the often troubled relationship between the public and police. If recording devices on regional airport officers can slash traveler complaints, how could they impact more serious matters?

Filming confrontations is not a cure-all. On Wednesday, a grand jury in Staten Island, N.Y., decided not to indict Officer Daniel Pantaleo in the death of Eric Garner, despite video showing Pantaleo putting Garner in an apparent chokehold. A medical examiner declared it homicide. Protests followed the Garner decision in cities across the country.

After a grand jury in Ferguson, Mo. decided not to charge officer Darren Wilson in the shooting of 18-year-old Michael Brown, President Obama proposed Monday reimbursing cities and towns for equipping local police forces with body cameras. The government would pay half the cost, requiring Congress to authorize $75­ million over three years.

Traveler grumbles have hushed at the Springfield-Branson National Airport, about 225 miles from Ferguson. “From twice a week or so to less than once per month,” Houseman said. “People can see the cameras, so maybe they act out less. Officers who know they’re being recorded tend to be on their best behavior.”

The president’s logic for funding body cameras nationally: Raw video will settle disputes, soothe tensions and prevent the kind of racial unrest that rocked Ferguson. More candid boosters claim the technology could help prevent police brutality. Detractors say it’s a government overstep, an invasion of privacy and an administrative nightmare.

This regional airport in Springfield, Mo., nestled in the Ozarks, offers flights to 11 U.S. cities — and a glimpse of how police forces across America could soon transform. Patrolling drastically changed, police supervisor Kevin Houseman said, once everyone was caught on video.

Early evidence suggests body cameras reduce patrol friction. Complaints against officers in Rialto, Calif. dropped 90 percent after the police force started wearing body cameras, according to The New York Times. Use of force also decreased. Arizona State University criminology professor Michael White found anecdotal evidence of a similar phenomenon in Phoenix but concluded more research is needed.

Under pressure of an intensifying policy push, the nation’s biggest cities are already moving to adopt the technology.

The New York Police Department starts testing body cameras this week, Mayor Bill de Blasio announced Wednesday. Washington police launched a pilot program in September and have already recorded hundreds of hours of footage. Los Angeles police plan to purchase hundreds of devices from Taser International, a company known for stun guns.

“Within the next five years or so, body-worn cameras will be as ubiquitous in the world of policing as handcuffs, the police radio, the gun,” Police Foundation president Jim Buerrmann told The Washington Post’s Max Ehrenfreund.

Even with government money, programs could get expensive, some police leaders fear. Body cameras run between $100 and $1,000. Storing hours of video, perhaps permanently, could also strain local budgets.

The Springfield-Branson National Airport body camera supply cost about $2,000, Houseman said: 11 devices for 11 officers. They store footage on airport computers.

They switch cameras on before each confrontation. The battery lasts an hour.

If a fight erupts, officers grab their tasers. They have never shot a suspect, Houseman said. A typical day combines customer service with parking tickets. Arrests happen about once per month, usually after someone picks a fight — or acts strangely and happens to be wanted.

“Usually, we’re dealing with people who have had a bad day — maybe their dog died, maybe they missed their flight — and they want to dispute a parking ticket,” he said. “They’ll say it was unfair, or that an officer was disrespectful to them.”

The video reveals the truth.

“We usually resolve these cases in less than a day,” Houseman said. “I watch the footage. I offer to show them the footage.”