The Evidence.com front page features a video plugging the service. Mostly it amounts to an endorsement from Salt Lake City Police Department Chief Chris Burbank, intercut with footage of the product in action. He extols the virtues of the platform, expressing particular gratitude about handing over responsibility for storing all manner of evidence to a private company.

The success of body cameras requires several assumptions. Advocates take it for granted that body cameras will positively affect police and citizen behavior, making the use of force less likely. They often cite a small number of real world trials involving police forces in California, Arizona, and Scotland. Proponents treat these examples as natural experiments proving that body cameras have a “civilizing effect.” In particular, the Rialto experiment has been deployed in recent debates as proof that cameras reduce the use of force (which dropped 60 percent there) and complaints against police (which were reduced by 88 percent).

But in a report this year for the U.S. Department of Justice, the criminologist Michael D. White cast serious doubt on what these examples prove. The only certainty across the studies were fewer citizen complaints about police misbehavior. Even if police find this outcome compelling, we don’t really know the cause. Was it because of changes in police behavior, public behavior, or some combination of the two? It’s even possible that behavior has nothing to do with it. White asks whether “changes in citizen complaint reporting patterns” might simply amount to a reduction in frivolous complaints. We might speculate that it’s also possible that citizens with a grievance are intimidated by the fact that police possess a record of their encounter to which the complaining citizen has no access.

To be confident about cameras’ effects on behavior, we’d need much more research, without which White thinks we can’t be confident about the upside of cameras. Meanwhile, we still have to worry about their downsides, including the knowledge that the trauma suffered by all parties as a result of a crime has been recorded. For police, there are a range of hidden costs associated with training, administration, and compliance in the roll-out of new technology. And manufacturers like Taser are banking on ongoing expenses long after the cameras have been bought.

Given that there are so many unanswered questions, where does the faith in these devices come from? As mobile, wearable technologies streaming data into the cloud, body cameras conform to what has become a preferred model of accountability and transparency in today’s culture. We entrust our personal exercise regime to Fitbits—and our working hours to productivity trackers—because we believe these devices are neutral observers, their output unimpeachable fact.

We have more faith in the devices that augment our work and leisure than we do in other people, or even ourselves. Humans are understood to be unreliable witnesses compared with connected digital devices. Contemporary wisdom says that while people create anecdotes, devices create data. We take it for granted that sensor metrics are capable of mitigating unruly human behavior—sloth, procrastination, discrimination, and violence.