If you’re listening to this while driving, there’s a chance you’ve passed an automated license plate reader.

ALPRs are cameras mounted on police vehicles or streetlights that scan license plates and feed that information into databases. But with more surveillance comes larger questions about who should be using this technology and for what purpose.

Rachel Levinson-Waldman is managing director of the Liberty & National Security program at the Brennan Center for Justice. She said this technology differs from cameras that can catch motorists in speed traps or running red lights because ALPR isn’t designed for issuing tickets. The following is an edited transcript of her conversation with Kimberly Adams.

Rachel Levinson-Waldman: Basically what they do is literally scan a car’s license plate, they log the date and the time of each scan, the license plate letters and numbers, the GPS coordinates — so there’s that location information — and then pictures of the car. That’s then fed back into a database, and most typically would be compared against a hot list. So that could include anything from stolen cars [to] Amber Alerts to outstanding warrants depending on the policy of the police department and any state law that comes into play.

Kimberly Adams: So to be clear, if you’re in a community that is using these ALPRs, anytime you drive by a police vehicle, your license plate and information could be gathered at that moment.

Levinson-Waldman: That’s exactly right. And I think that brings up a really important point, which is that it has nothing to do with suspicion. But nevertheless, they’re indiscriminately scanning all of this data and keeping it for anywhere from a few seconds up to multiple years, depending on the policy and law in place.

Adams: I imagine a lot of folks don’t know that this technology is even being deployed in their communities. How widespread is it in the United States?

Levinson-Waldman: So we don’t have recent numbers. but what we do have suggests that they’re in pretty high use. As of 2013, over 90% of police departments in cities and urban areas with populations of over a million — so 16 cities and urban areas — used their own ALPR systems. And police departments often integrate this kind of technology into what are called real-time crime centers. So [they] could be combining license plate data with surveillance footage from cameras, whether that’s police cameras, school cameras, traffic cameras, gunshot-detection systems, even social media monitoring. And a number of cities do have real-time crime centers, so we’re talking about cities like New York, D.C., Austin [Texas], Miami — a number of cities across the country.

Adams: Police departments use ALPR, as you’ve just laid out. Who else is implementing this technology?

Levinson-Waldman: So we know that ICE, Immigration and Customs Enforcement, an arm of the Department of Homeland Security, has accessed ALPR data. And there’s also a significant private industry. So a lot of police departments contract with vendors that give them access to private databases that have scans, even from other law enforcement agencies. So you see, sometimes this plate data is kind of able to go through pretty significant networks of sharing.

Adams: What are some of the privacy concerns associated with this type of surveillance?

Levinson-Waldman: The Supreme Court has held pretty clearly that because vehicles are heavily regulated, which includes having to display a license plate, and because vehicles on public roads could be seen by any member of the public, there’s just no expectation of privacy in the context of license plates. We also see police departments regularly sharing ALPR data with one another. And in a number of states, there just aren’t any laws that regulate how police departments can share that data, so it’s just left to the discretion of individual departments. And there have been real concerns about how these devices can be used to intrude on privacy and to intrude on exercise of constitutional rights.

Adams: What concerns are there about how this tip could be used in a post-Roe [v. Wade] environment?

Levinson-Waldman: Police don’t need a warrant to obtain this kind of information. And so you can map out a lot of travel patterns using license plate data, right? It kind of depends how comprehensive a license plate reader network is or if you’re combining this license plate data with other information. So for instance, cellphone-tracking information, information that’s released to the apps that people have on their phones, things like that. Especially with the incredibly restrictive laws that we’re seeing, which criminalize so many of those associated activities, it becomes really dangerous to have that license plate reader data in hand.

Related links: More insight from Kimberly Adams

Levinson-Waldman co-authored a Brennan Center white paper on ALPR. In it, they advise police departments to implement greater transparency and oversight so third-parties can evaluate how responsibly this tech is used.

In the wake of the Supreme Court’s decision to overturn Roe v. Wade, lots of tracking technology is getting a closer look. But unlike an app or a website, you can’t necessarily delete, avoid or opt out of the ALPR network.

Wired has a story on how these systems could be used for tracking those seeking abortions and more details on the network of data sharing between law enforcement and private systems, say, a homeowners association that puts up ALPRs in the neighborhood.

Flock Safety, a private firm with systems in about 1,500 cities, provided a statement to Wired saying it doesn’t sell or share data with third parties.

“While we cannot speak for any other vendors, we have never and will never sell data to repossession companies or third-party organizations, including anti-abortion groups.”