If it weren’t for the photograph, Mike Katz-Lacabe probably wouldn’t remember getting out of his car on November 14, 2009.

“The timing was just magnificent: where my daughters and I were getting out of the car in our driveway,” he said. “There is a very clear image of that, you can recognize all of us, getting out of the car in the driveway.”

The San Leandro Police Department captured this photo of Mike Katz-Lacabe and his daughters in front of their home on November 14, 2009. Credit: Mike Katz-Lacabe

The San Leandro Police Department captured this photo of Mike Katz-Lacabe and his daughters in front of their home on November 14, 2009.
Credit: Mike Katz-Lacabe

The photograph was taken by the San Leandro, California police department. Or more accurately, by an automatic camera that sits on the top of a San Leandro patrol car, and constantly snaps pictures of cars in the city.

Katz-Lacabe has never been convicted of a crime: he’s not a suspect in any case—he’s just a normal, taxpaying, married, father of two. He’s lived in this San Francisco Bay Area town for over 20 years, and has been on the school board since 2006. In his spare time he enjoys hiking with his daughters.

And yet, the San Leandro police department has what amounts to a family photo album of him and his car.  More than 100 pictures taken between 2008 and 2010.

“There was one of me by the library, there was one of my car parked by a friends’ house,” Katz-Lacabe noted.

If you drive a car and live in an American city, well, your local police department probably has an album of you, too.

License plate reader technology has been around since the 1980s. But about a decade ago, police and other law enforcement in the US started using license plate readers to track cars. These specialized cameras scan every single car that passes in front of the camera, in any direction, and they typically do it at astonishing speeds: 60 license plates per second.

The camera automatically checks the license plate against a ‘hot list’ of stolen cars. Police can use the scanned information, plus the date, time, and precise GPS location—to pull a car over. Or they can just keep the information. Sometimes forever.

At a City Council meeting last fall, San Leandro Police Chief Sandra Spagnoli explained how the city has been using its three license plate readers.

“[We were] able to ID home robbery suspect by entering info,” she said. “In January 2013, [we caught a] wanted felon after hit from LPR, all on one vehicle we’re talking about. May 2011, robbery suspect…homicide suspect, wanted in Nevada, and arrested in 2011.”

She says using cameras has helped reduce crime all around the Bay Area.

“What we’re seeing is other systems, coming online: Piedmont, Alameda Co Sheriff, Oakland, crime can be displaced. Look at cities around us, and the concern is the displacement of crime into San Leandro.”

The question—as with much of law enforcement—is how to balance protecting a community with protecting our constitutional right to privacy.

“Does it invade reasonable expectations of privacy for the police to monitor our whereabouts when we’re in public spaces?” asked Linda Lye, an attorney with the American Civil Liberties Union of Northern California. “It’s a really fascinating intellectual and constitutional question of the notion—does privacy in public space exist? Civil liberties advocates really argue vehemently yes.”

We went driving around the city border between Oakland and Piedmont to look for Piedmont’s license plate readers. It didn’t take us long before we found the cameras pointed down at her car, mounted on overhead poles.

Her argument is that somebody like Mike Katz-Lacabe has a right to privacy, even if he’s standing on the sidewalk, and I should have that right, too, even if I drive down the street.

“Just because I’m outside my private house doesn’t mean I’ve surrendered all rights to the state to be monitored and tracked as I go about my daily life engaging in no wrongdoing whatsoever and in some cases engaging in constitutionally-protected activity,” she added. “So the law enforcement, the traditional 4th amendment line has been drawn between a public space and a private space. If you’re walking on the street, the police don’t need a search warrant.”

The Fourth Amendment—that’s the one that protects us from illegal search and seizure—is usually interpreted to mean that there is no reasonable expectation of privacy in public. In 1983, the Supreme Court concluded in US v. Knotts, that “a person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another.”

License plates are obviously visible in public. So in theory, it’s totally fine to use machines to capture information about a license plate. Even if those machines capture that information orders of magnitude faster than any person could.

There have been a number of lawsuits that uphold the use of license plate readers. And many in law enforcement see no problem with them. In 2006, a New York State agency told local police it saw “no impediment to the use of a license plate reader by law enforcement.”

But three years later, the International Association of Chiefs of Police warned that license plate readers could raise privacy issues. The group advised law enforcement to restrict use of the data to what it calls “official use only.”

The ACLU’s Linda Lye says her biggest worry is about is the so-called ‘mosaic theory.’ This idea says it’s possible to get a pretty clear picture of a person by putting together lots of small bits of information.

“Like clockwork, do they go home at 8 o’clock every night but then every now and then on a Friday evening they don’t go home?” Lye asked. “On Sunday morning they’re a faithful churchgoer, but then on some Sundays they don’t go to church. So what does this tell us about infidelity, about medical conditions, about political associations?”

Before license plate readers, the only way for the cops to know where any of us were at any given time was to notice us (or our license plates) and somehow make a record of it. That was something that rarely, if ever, happened. Now, though, cops can easily get a fairly accurate—if rough picture—of where we’ve been over time.

That can be useful if you’re trying to find out where a bad guy hangs out, or whether an alibi holds water.

But it could also let police draw wrong conclusions. I often drive through a section of East Oakland that is known for great Mexican taco trucks—and a lot of night-time prostitution. An overzealous cop could easily misinterpret my love of tacos for a love of something less savory.

“In the pre-technological era, resources was a basic, natural protection for privacy that law enforcement simply didn’t have the resources to compile detailed information about us unless they had a very good reason,” Lye concluded. “Now, it can be done on the basis of idle curiosity.”

There’s also a very real question about how useful all this data is. One study suggested that nearly 40-percent of big police departments use readers.

But much like the NSA, which collects meta-data from cell phones and elsewhere, law enforcement now has more information than it can realistically use. Plus, everywhere these readers are used, every car is likely getting scanned many many times. In the case of San Leandro, a town of just 85,000 people, one license plate reader on one car captured one million records in a single year.

Last year, the ACLU looked at data from Maryland and found that out of 42 million scans, the hit rate was 0.2 percent. Take out minor violations like expired registrations, and the hit rate goes even lower: for every million plates read, 47 were flagged for possibly being a stolen car.

It’s hard to know how other states stack up, because there’s so much secrecy around the use of these readers. I requested data on my car from the police departments in Oakland—where I live—Berkeley, San Francisco, Los Angeles, and my hometown: Santa Monica, California. I also requested the same data from Sheriff’s offices in nine counties across the Bay Area and Los Angeles.

In some cases, such as the LAPD and LA Sheriff’s Department, they refused to even tell me whether they had such data at all.

Earlier this month, the City of Piedmont (which is right next to Oakland) refused to give me the license plate reader records on my own car, citing privacy reasons.

It seems that this technology is only going to grow. But it’s also easy to get hung up on the use of license plate readers.

New technology, like facial recognition, is being developed all the time. Which will make it easier to identify us by other means. And that me wonder: if there’s no expectation of privacy about where my license plate has been, what about my face?

Cyrus Farivar [suh-ROOS FAR-ih-var] is the Senior Business Editor at Ars Technica, and is also an author and radio producer. He first began reporting on license plate readers 2012 and has become, admittedly, a little obsessed. Read his prior work on this subject here:

The cops are tracking my car, and yours (July 18, 2013)

Your car, tracked: the rapid rise of license plate readers (August 15, 2012)

Minnesota modifies liberal open records law to make car location data private (March 19, 2013)


How has surveillance changed the way we live with the law? Elizabeth Joh teaches Criminal Procedure at UC Davis Law School. In an interview with Life of the Law’s Executive Producer, Nancy Mullane, Joh says an increase in the use of private police and surveillance in the US has made many people numb to the fact they are being watched.

Policing by Numbers: Big Data and the Fourth Amendment, 89 Wash. L. Rev. 35 (2014) (symposium).

From Anti-Drone Burqas To Face Cages: What Artists Are Showing Us About Surveillance and the Law, The Life of the Law, April 2, 2014.

Will Big Data Change How Police Do Their Job?, The Life of the Law, Nov. 6, 2013.

Maryland v. King: Three concerns about policing and genetic information, Genomics Law Report, Sept. 19, 2013.

Top Image Credit: Aurich Lawson