When Alameda County sheriff’s deputies reportedly beat a car-theft suspect after a high-speed chase from Castro Valley last fall, the onslaught of blows was not the only troubling revelation. None of the 11 deputies at the scene turned on their body cameras.

If it weren’t for a private overhead security camera, there would have been no video record of deputies pummeling a cowering Stanislov Petrov. The episode highlighted how the accelerating adoption of body-worn cameras by Bay Area police still leaves a central question only partially answered: How — and how often — should they be used?

This news organization surveyed dozens of local police departments about their body camera policies. Of the 48 agencies who responded or had available records, 31 have deployed or approved body cameras, and an additional eight are planning to. Twenty-nine of the 31 have established policies calling for the body cams to be running as much as possible.

But in practice, officers are still the primary arbiters of when the cameras start rolling, which concerns accountability advocates. And none of the dozen policies reviewed by this news organization prescribed specific penalties for failure to turn the cameras on.

“The cameras can’t improve accountability and public trust if officers can turn them off at will or on the fly,” said Catherine Wagner, a staff attorney for ACLU of Southern California. “They can’t self-edit.”

The Alameda County case was a wake-up call for the Sheriff’s Office, which had been in the process of updating its camera policies and fast-tracked revisions afterward, including making their use mandatory. In the purported beating incident, one officer’s camera inadvertently activated, but it revealed little about what happened.

“When 11 body cameras aren’t turned on, I think that’s cause for concern within the organization and the community,” sheriff’s Sgt. Ray Kelly said.

Of the region’s three largest cities, only Oakland deploys the cameras; San Francisco and San Jose expect to begin using them this summer.

Nearly two-thirds of the 48 departments that responded to the survey or had public body-camera documents available have simple instructions about body cameras: Use them. In essence, short of clear privacy exceptions such as inside a hospital room, specific surveillance exceptions or idle time, the cameras should be rolling.

Part of making it instinctive could just be a matter of repetition. Campbell police Capt. Joe Cefalu, whose department in 2008 became one of the first in the state to outfit its officers with body-worn cameras, recalled that officers initially were hesitant about using the cameras. It took time for them to get into the routine of turning them on, which typically can be done with the slide of a switch or a quick button press.

“Now it’s ingrained in our culture, especially with officers who came after. They only know law enforcement with a video camera,” Cefalu said. “We want to record more than what we don’t record. Anything that might be of an enforcement nature.”

Failing to turn the cameras on can have broad repercussions in sorting out critical incidents. In July, for example, Pleasanton police Officer Daniel Kunkel shot and killed San Jose resident John Deming Jr. in a highly disputed case muddled by a shifting police account of events. Kunkel told investigators that his camera typically didn’t work and that he was too busy focusing on the initial burglary call that summoned him.

Lt. Brian Laurence, a spokesman for the Police Department, declined to say whether Kunkel was disciplined for not turning on his camera.

Last year, Menlo Park police began requiring officers to turn on cameras regularly, rather than only in the most critical situations. This came at the behest of the City Council after an officer-involved shooting was not recorded because it started as a burglary call.

A review of more than a dozen agencies’ policies for body cameras — they tend to be similar and are often modeled after a countywide template, which is the case in Santa Clara County — reveals that none prescribes specific discipline for failing to turn on a body-worn camera. Any lapses would likely already be covered by existing rules governing policy violations, and the technology is still so nascent that some departments have opted against punishment to make officers more receptive to the devices.

Rather than making camera use mandatory, as most agencies have done, San Leandro and San Ramon explicitly authorize officer discretion about when to turn them on, as a hedge against the unpredictable nature of police encounters.

“Some of the agencies that had that mandatory turn-on policy, officers were getting disciplined because they forgot to activate,” Lt. Robert McManus, of San Leandro, said.

McManus added that withholding harsh penalties as officers learned the ropes of using the cameras yielded a threefold increase in activations in two years.

Cefalu says that, regardless of whether departments call for “discretionary” or “mandatory” use, officers ought to keep their cameras on in anticipation of how quickly a seemingly innocuous contact can go sideways.

“Officers need to be recording everything we can rather than only when you think so. Anything that could lead to confrontation, assault, any enforcement, we have to make every reasonable effort,” Cefalu said. “Sometimes you won’t be able to, because things happen fast. But that’s the exception, not the rule. It’s for the public’s protection, and for officers’ protection.”

Having taken lessons from the Petrov case, the Alameda County Sheriff’s Office is now looking to lead the push for maximizing recording.

“Anytime that they have contact with a member of the public, they will turn on their cameras. And the only time they will not turn on their cameras is when there are privacy issues or decency issues,” Kelly said. “If you have an officer who has repeated violations of not turning their camera on, then you may have a discipline situation.”

San Jose police Lt. Elle Washburn, who oversees that city’s camera program, said officers’ primary concern should be that they’re recording.

“What will get you in trouble is when you’re supposed to have the camera on and you don’t,” Washburn said. “The department will have to set precedent for when someone is misusing the system. It may be retraining. We expect to have some margin of error — that is human nature — but that is going to taper off with time.”

Wagner, the ACLU attorney, contends that even citizen objections to the cameras need to be recorded, such as when a witness expressly asks not to be on camera.

“We want to minimize discretion in most circumstances. It’s important that the request itself to turn the camera off is recorded, so it’s clear it wasn’t the officer’s idea or failure to record the conversation,” she said. “For those encounters, if there’s a way to continue audio recording, that should be done.”

Many of the results of body-worn cameras have been promising: Oakland’s documented uses of force by police plummeted by two-thirds in four years. But in some cases, video from body cameras failed to bring the clarity it’s thought to provide, such as in the case of a fatal 2014 shooting by San Jose State police. The police and the family of the man who was shot saw the same body-camera footage and remained diametrically opposed in their beliefs about what happened.

But none of that can happen if the cameras aren’t on, advocates say.

Walter Katz, San Jose’s independent police auditor who previously served as a police watchdog in Los Angeles County as deputy inspector general, said he recognizes that policies can’t cover every fast-moving scenario but that the situation is not unlike most situations officers encounter. He compared it with activating a police vehicle’s lights and sirens, for which there are enshrined policies, but officers are essentially entrusted to use reasonable judgment.

“You expect officers to exercise discretion with nearly everything. Still, they have to exercise it within a very narrow confine,” he said. “This is just learning another thing they have to do. They’re capable of doing that.”

Contact Robert Salonga at rsalonga@bayareanewsgroup.com. Contact Dan Lawton at dlawton@bayareanewsgroup.com.