RIALTO, Calif. — “Get on the ground,” Sgt. Chris Hice instructed. The teenage suspects sat on the curb while Sergeant Hice handcuffed them.
“Cross your legs; don’t get up; put your legs back,” he said, before pointing to the tiny camera affixed to his Oakley sunglasses. “You’re being videotaped.”
It is a warning that is transforming many encounters between residents and police in this sunbaked Southern California city: “You’re being videotaped.”
Rialto has become the poster city for this high-tech measure intended to police the police since a federal judge last week applauded its officer camera program in the ruling that declared New York’s stop-and-frisk program unconstitutional. Rialto is one of the few places where the impact of the cameras has been studied systematically.
In the first year after the cameras were introduced here in February 2012, the number of complaints filed against officers fell by 88 percent compared with the previous 12 months. Use of force by officers fell by almost 60 percent over the same period.
And while Mayor Michael R. Bloombergrailed against the federal court, which ordered New York to arm some of its own police officers with cameras, the Rialto Police Department believes it stands as an example of how effective the cameras can be. Starting Sept. 1, all 66 uniformed officers here will be wearing a camera during every shift.
William A. Farrar, the Rialto police chief, believes the cameras may offer more benefits than merely reduced complaints against his force: the department is now trying to determine whether having video evidence in court has also led to more convictions.
But even without additional data, Chief Farrar has invested in cameras for the whole force.
“When you put a camera on a police officer, they tend to behave a little better, follow the rules a little better,” Chief Farrar said. “And if a citizen knows the officer is wearing a camera, chances are the citizen will behave a little better.”
Despite concerns about privacy and cost, more citizens across the country will probably soon find themselves on camera when talking to the police.
Albuquerque, Fort Worth and Oakland have all begun arming officers with tiny video cameras. And demand for the devices has exploded in recent years, according to Taser International, one of the companies marketing body cameras to law enforcement agencies.
Experts increasingly say that body cameras are likely to become an industry standard over the coming years, just as cameras in patrol cars, which once prompted similar objections about privacy, have become commonplace in recent decades.
William J. Bratton, who has led the police departments in New York and Los Angeles, said that if he were still a police chief, he would want cameras on his officers.
“So much of what goes on in the field is ‘he-said-she-said,’ and the camera offers an objective perspective,” Mr. Bratton said. “Officers not familiar with the technology may see it as something harmful. But the irony is, officers actually tend to benefit. Very often, the officer’s version of events is the accurate version.”
Still, the technology has proved divisive. Police officers and citizens alike have bristled at what they see as the latest incursion of Big Brother. In New York City, the Patrolmen’s Benevolent Association called the equipment “an encumbrance.” Privacy advocates worry that video of police officers searching a suspect’s home could end up on the evening news.
“The body camera issue opens up certainly more questions than it answers,” Raymond W. Kelly, the commissioner of the New York Police Department, said Sunday on “Face the Nation.” “The only place that this has been implemented are cities that are much, much smaller.”
Mr. Bratton acknowledged the difficulties that would be involved with phasing in body cameras in a large police department like New York’s, which employs about 35,000 uniformed officers.
At up to $900 per camera, the cost of phasing in officer cameras in major cities promises to be immense. While he was police chief in Los Angeles, from 2002 to 2009, Mr. Bratton pushed to have cameras installed in squad cars, after a recommendation from the federal monitor. But it took years, and $5 million, to outfit less than a fifth of the department’s fleet with cameras.
Nonetheless, police officials from Oakland to Greensboro, N.C., all cited the swift resolution of complaints against officers as one of the primary benefits body cameras had offered. In some cases, citizens have come to the police station to file a complaint and decided not to after they were shown the video of the incident.
In other cases, though less frequently, officials said, accusations of officer misconduct have been corroborated by video from body cameras.
“It’s definitely not cheap,” said Paul Figueroa, an assistant chief with the Oakland Police Department. “But over the long term, just from a liability and management perspective, it’s definitely an investment that’s worth it.”
Thus far, the American Civil Liberties Union of Southern California has not received any complaints about police body cameras. And despite privacy concerns, the organization supports increased used of the technology.
“Cameras hold real promise for making it easier to resolve complaints against police,” said Peter Bibring, a senior lawyer with the A.C.L.U. of Southern California. “They do raise privacy concerns, but ones that can be addressed by strong privacy policies.”
Mr. Bibring said that video should not be stored for prolonged periods, except in cases of alleged misconduct, and at least some video, like searches of private homes, should not be made available to the public.
Thus far, though, almost every department has handled officer cameras differently. With about 450 cameras for 620 officers, the Oakland Police Department is one of the largest agencies using them; it stores video indefinitely.
Next month, the Police Executive Research Forum will host a conference on officer body cameras, with the goal of developing best practices for departments across the country.
Rialto’s experience offers other cities a lot to emulate.
During the yearlong study, half of the city’s patrol officers were randomly assigned to wear body cameras each week, and instructed to turn them on whenever they made contact with a civilian.
Officers used force 25 times, down from 61 over the previous 12 months. And those wearing cameras accounted for 8 of those incidents.
Sergeant Hice said he has come to view the camera as a kind of protection. The video would show the two teenagers running through the field matching the description he was given, he said, and that he did not use excessive force while detaining them.
“It captures what’s really occurring in real time,” he said. If the suspects later “think of a good story, with bits of detail thrown in to enhance a false story,” he added, “we can dispel it.”