“People with borderline personality disorder have a very difficult time identifying when distress is very high,” said Lynn McFarr, director of the cognitive and dialectical behavior therapy clinic at Harbor U.C.L.A. Medical Center, which provides care for people in the Los Angeles County system. “If we can show them, in this biofeedback fashion, that the signals went off the rails yesterday, say, after they got into a fight with a co-worker, then they’d be able to anticipate that emotion and target it with the skills they’ve learned.”

The potential for digital technology to transform mental health care is enormous, and some 10,000 apps now crowd the market, each promising to soothe one psychological symptom or another. Smartphones allow near continuous monitoring of people with diagnoses such as depression, anxiety and schizophrenia, disorders for which few new treatments are available. But there has been little research to demonstrate whether such digital supports are effective.

California’s collaboration with Silicon Valley is an attempt to change that : in effect, enlisting some of the state’s most privileged residents to help some of its least . California has set aside taxpayer money to pull it off, more than $100 million over five years. If Big Data can help manage persistent mental distress, the path forward is likely to run through the Golden State.

But if early signs are any indication, the road will be slow and winding, pitted with questions about effectiveness, privacy and user appeal . At least for now, California’s effort to jump-start medicine’s digital future is running into some of the same issues that have dogged old-fashioned drug trials: recruiting problems, questions about informed consent, and the reality that, no matter the treatment, some people won’t “tolerate” it well, and quit.

“We need to understand both the cool and the creepy of tech,” said Keris Myrick, chief of peer services for Los Angeles County, who has been deeply involved in the collaboration. Ideally, she said, the apps could give people personalized tools to manage their distress and take pressure off the mental health system. But using them means sharing personal data with private companies, and any “fire alarm” has the potential to trigger anxiety, as well as blunt it. “We want to make sure people have the information to use the apps safely , that they have some digital literacy, and that their privacy is protected,” Ms. Myrick said.