Illustration: Aïda Amer/Axios

Residents of major American cities are constantly watched by ubiquitous cameras, mushrooming license plate readers and a battery of new smart city sensors.

But, but, but: It's not just the government keeping tabs. An explosion of private surveillance — set up by businesses, landlords and neighbors — is being driven by increasingly cheap but powerful technology. And what these observers see could make its way back to law enforcement.

Big picture: Old-school video cameras have long watched over stores and gas stations. Now, a new wave of technology, once too expensive and complex to be used by anyone but the police, is making its way into mom-and-pop shops, front porches and residential streets.

  • Video cameras that flag unusual movements and recognize faces are being stuffed into popular "smart" doorbells that constantly send footage to the cloud.
  • AI-powered "video analytics" can identify specific actions like smoking, and search thousands of hours of archived footage for one person. It's popping up in public schools, like in Broward County, Fla., which includes Parkland.
  • License-plate readers are now guarding the entrances of wealthy neighborhoods, tracking every vehicle that passes and automatically flagging blacklisted cars.

"We're seeing a growing adoption of home security technology as a part of a digital neighborhood watch," says Mana Azarmi, policy counsel at the Center for Democracy and Technology. "These technologies can be abused by stalkers, criminals and suspicious spouses."

Driving the news: At least 10 neighborhood homeowner's associations in the Denver area have bought license-plate readers to monitor every car coming in and out, reports Elise Schmelzer for the Denver Post. The cameras also record the faces of passersby.

  • The technology, which now costs only a couple hundred bucks to set up, is also being taken up by landlords that rent to low-income communities — often to police their own tenants.
  • One security company uses 475 cameras to watch over hundreds of properties, flagging guest-policy violations, parking lot collisions and illegal dumping, reports Josh Kaplan for Slate.

The data that private security systems gather are often open for law enforcement to dip into, potentially allowing police to get around restrictions on government surveillance that don't apply to private citizens, privacy experts say.

  • "If the only regulation on police is on what they can do with their own equipment and their own license-plate technology, it becomes trivial to avoid that," says Nathan Freed Wessler, an ACLU staff attorney.
  • In that case, Wessler says, police "have access to an incredible compendium of Americans' movements across time and space, going back years, potentially."
  • Some departments, savvy to this symbiotic arrangement, subsidize the price of video cameras in return for access to residents' surveillance archives.

What's next: Some states, including New Hampshire and Utah, have passed laws limiting police access to private plate-scan databases. But curbing purely private surveillance is difficult, legal experts tell Axios, because the First Amendment protects photography in public places.

Go deeper: Private license-plate readers help police and lenders target the poor (The Atlantic)

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