Clayton Burnett seems like an unlikely candidate to run a cutting-edge surveillance system. He is not an FBI agent, nor does he investigate homicides for the NYPD. Burnett is the director of innovation and new technology at Watchtower Security, a private company that contracts with property managers—hundreds of them—in low-income communities across the U.S. About three years ago, his company started contracting with OpenALPR, a startup whose software lets users track people by their license plates. “The price point was very reasonable for us,” Burnett says, so now Watchtower has more than 475 cameras scattered across its properties—he says they sometimes scan more than 1.5 million license plates in a week. With just a quick search, now Watchtower can see every time someone passed by one of its apartment complexes in the past two months.

Burnett’s company regularly hands over location data to police, he says, as evidence for cases large and small. But that investigative firepower also comes in handy for more routine landlord-tenant affairs. They’ve investigated tree trimmers charging for a day of work they didn’t do and caught people dumping trash on private property. Sometimes, he says, a tenant will claim her car was hit in the building’s parking lot and ask for free rent. His company can search for her plate and see that one day, she left the lot with her bumper intact and then came back later with a dent in it. Probably once a week, Burnett says, Watchtower uses it to prove that a tenant has “a buddy crashing on their couch,” violating their lease. “Normally, there’s some limit to how long they can stay, like five days,” he says, “and we can prove they’re going over that.” One search, and they have proof that that buddy has been coming over every night for a month.

I was wondering how tenants felt about this, and I asked Burnett whether anyone had ever complained about the license plate readers. “No,” he said with a laugh. “I’d say they probably don’t know about it.”

Automatic license plate readers, or ALPRs, have been part of law enforcement’s toolkit for well over a decade. However, the technology has evolved rapidly in the past couple of years, radically changing who is able to access ALPRs and what they’re able to do with them. Startups like OpenALPR (recently acquired by Rekor) and Flock Safety have jumped into the scene. The software now can read much more than license plates. It can detect dents on cars. It can search for specific bumper stickers and for Lyft tags. And while until recently, acquiring ALPRs meant buying custom-built cameras that cost at least $10,000 a pop, OpenALPR is strictly a software company. Its system works with any internet-enabled camera (one user I spoke to purchased “really good” cameras for less than $150 each), and licenses cost less than $100 per device. Matt Hill, founder of OpenALPR, says that one city (he wouldn’t name it) recently purchased 1,000 licenses. The city already had traffic cameras in place, so all it had to do was buy the software.

And as the technology has matured, it’s gotten in the hands of organizations that, five years ago, would never have been able to consider it. Small-town police departments can suddenly afford to conduct surveillance at a massive scale. Neighborhood homeowners associations and property managers are buying up cameras by the dozen. And in many jurisdictions, cheap ALPR cameras are creeping into neighborhoods—with almost nothing restricting how they’re used besides the surveiller’s own discretion.

I talked to about a dozen people who use ALPRs, everywhere from California to Alabama: property managers, small-town police chiefs, and people who’d simply gone Dutch with their neighbors to buy some software. Almost all of them had started using it in the past three years, drawn by its sudden affordability. John Hudson is a contractor working with police in Allegheny County (the area surrounding Pittsburgh), and he says that Allegheny law enforcement first tried out the technology in 2010. Back then, the cameras ran $10,000 a piece. “At that time, we were only able to install a couple cameras,” he says. “We’re not New York. We just don’t have the money to afford that type of technology.” Hudson says no one found the cameras particularly useful at that point.

That changed about 2½ years ago, though, when the Allegheny district attorney decided to buy OpenALPR licenses. Hudson now has almost 400 cameras installed around the region, and he says that’ll probably rise to 500 by the end of 2019. The change in scale has turned ALPR from a neat trick to a game-changing technology. Police use it for everything from DUI cases (was she swerving before we pulled her over?) to kidnappings. Recently, Hudson says, they used license plate readers to “virtually gate” McKeesport, a low-income, 20,000-person town south of Pittsburgh: “Any way you can come in and out, you’re on camera.” The dream behind ALPR has finally come true in Allegheny County: Police can actually track someone as they move around the region. “We used to have it on main corridors used for drug trafficking,” Hudson says. “Now we’re going into neighborhoods.”

ALPRs can change how departments police—they can change the level of crimes that they go after.

Now that ALPRs have proliferated across cities, officers tell me they’ve become a much more effective tool for combating crime. But they also now have far more potential for abuse. Dave Maass, who has worked closely on ALPRs at the Electronic Frontier Foundation, a civil liberties advocacy group, says he is particularly concerned about the sensitive information being swept up by plate readers: “If people saw a cop sitting in front of their church or their oncologist writing down license plates, people would be concerned.”

This is not merely a hypothetical concern. A few years ago, the Associated Press reported that NYPD used ALPRs to scan the plates of worshippers at a mosque. Police in Edmonton, Alberta, admitted to using a confidential police database in 2004 to get the plate number of a local columnist who was sharply critical of police conduct and ordering officers to look out for his car, hoping to catch him at a bar and then arrest him for drunk driving. Maass thinks no one should be able to query an ALPR system without a warrant. “Now a cop can look up your license plate and see where you’ve been for the past two years,” he says. “This may be used to track journalists and find out who their sources are. This may be used to find out who’s going to a protest.”

Police officers have also been caught abusing law enforcement databases for personal reasons, like illegally stalking girlfriends and looking up women they find attractive. When I asked him about this concern, Hudson said they’d had a “complaint” at one point, but he declined to go into details: “Don’t want to share dirty laundry with you.” But he says his department addressed the problem by implementing an auditing system. Now, it proactively monitors what officers search for to ensure that the system’s used only for work purposes.

However, other people have doubts about how effective an audit system can be. Maass says that in California, anyone who uses ALPRs is required to have a policy online, but some agencies have simply put policies on their websites without ever actually implementing the auditing they claim to do. And even when auditing does happen, several employees told me they’re not confident that it works. One officer, who recently left a large sheriff’s department in Minnesota, told me that his department seriously monitored ALPR use and he’d never heard of anyone abusing the system. He wasn’t sure that that meant it hadn’t happened, though. “In our department, there’s probably a 50-50 chance you’d get caught,” he told me. He paused. “Ah, that’s optimistic.”

Even when used properly, ALPRs can change how departments police—they can change the level of crimes that they go after. Garrett Langley, the CEO of Flock Safety, told me that this is one of the technology’s selling points: “Issuing a BOLO [“Be on the lookout”] for a nonviolent crime is just not cost-effective.” If you know that a bald guy in a gray Toyota illegally dumped trash in your lawn, the police won’t try to track him down. But if they have the plate, enforcing lower-level crime becomes much easier. Several of the property managers and homeowners associations I spoke to emphasized that this is one of the main benefits of their ALPR systems. Along with burglaries, they’re mostly concerned about people breaking into cars to steal personal belongings; police wouldn’t investigate that before, but now homeowners associations can do the investigation for them and hand over the evidence. As Burnett put it, “[Police] are not going to be able to investigate [a small crime] unless we hand it to them on a silver platter. Which we’ve done plenty of times.”

As for their own ALPR cameras, some of the law enforcement agencies I talked to were only using the system for felony investigations: “the worst of the worst.” But others used it more expansively. Driving with suspended license. Vandalism. “Immigration violators.” (According to the ACLU, more than 80 local law enforcement agencies share their license plate data with Immigration and Customs Enforcement.)

“[There’s] no scope whatsoever,” the Minnesota officer told me. “We used it whenever it seemed useful.” He’s used ALPRs to investigate “literally everything,” from terrorism to shoplifting to $200 credit card theft. “That said, I’d never investigate $200 credit card theft if it wasn’t linked to a dozen others,” he clarified. But he also says that ALPR makes it much easier to connect petty crimes together. He’s worried that this might exacerbate bias in the judicial system, leading to selective overenforcement. Police may install cameras in a neighborhood to investigate violent crime but then end up catching a disproportionate number of petty crimes in the process. “Even if we had a few cameras in our high-crime neighborhoods, we could solve a ton of crimes,” he said. “But there are a lot of racial and privacy concerns with putting cameras in a specific area.”

Brock Boone, an attorney with the ACLU’s Alabama chapter, thinks this may already be happening in his state. “Anecdotally, it seems to be that these are put up in neighborhoods with people of color,” he says. “We would just need to see the data.” But he says that he and his colleagues just haven’t had the capacity to seriously look into how Alabama police use the technology, let alone push for reforms. “There are huge privacy implications of this data collection,” Boone says. But “we just don’t have the resources that the ACLUs in New York or California have, or even Michigan.”

As automatic license plate readers proliferate in smaller towns and redder states, there are not always organizations in place ready to push back against them. And this means that police and property managers are left to regulate themselves. Sara Rose is an attorney for the Pennsylvania ACLU in Allegheny County, and she’s been involved in a bill that would provide some basic restrictions on ALPR in her state (although not nearly enough, in her opinion). I asked her if she was aware of the “complaint” about misconduct that Hudson had mentioned to me. She hadn’t been. “But I think it shows the need for government entities to put policies in place to prevent misuse of this technology before they start using it rather than after the fact,” she told me. “We’re just missing very basic limits on what police can do with this.”

And for insurance companies and nosy neighbors, those limitations are almost nonexistent. Valerie is part of a homeowners association in West Los Angeles that began considering ALPRs after a series of break-ins in the area. “Mostly just into cars,” she says. “Break the windows and steal sunglasses or whatever.” She and her neighbors considered other options first, like hiring a private patrol car for the neighborhood, but that seemed too expensive. So a few weeks ago, her block joined together to buy two Flock Safety cameras—enough to see every time a car entered or left their street. They split the cost, so she says each house only has to pay about $130 a year, and two of her neighbors volunteered to monitor the system. There was one holdout, however. “One neighbor thought it was a violation of his privacy,” she told me. I asked her if she thought he’d ever come around to it. “No,” she responded. “We just leave him alone.”

Future Tense is a partnership of Slate, New America, and Arizona State University that examines emerging technologies, public policy, and society.