A recent Supreme Court ruling which found that cell phone location history searches require a warrant could have a ripple effect on the use of automated license plate readers (ALPRs), some legal scholars and ALPR opponents say.
Last month’s Chatrie v. United States ruling — the first major Supreme Court Fourth Amendment case in eight years — addressed fundamental questions about law enforcement’s use of private data. Over the past several years, police have been pressuring big tech firms to turn over users’ location history data so that they can pinpoint which phones were in the area of a crime scene during a particular time period.
The Supreme Court ruling suggests these “geofence” searches are protected by the Fourth Amendment, and opens the door to a debate about potential parameters for how police can use them in the future.
If a warrant is ultimately needed for ALPR searches, experts say, it would radically limit how the networks of cameras can be used and would change modern policing.
Flock Safety, the country’s leading ALPR vendor, has between 90,000 to 100,000 cameras installed on public roadways and collects data on about 20 billion license plates a month, it says. Police increasingly use the data collected by these cameras to identify suspects.
Although the Chatrie case involved Google — which gave police a list of the phones inside the so-called geofence where a crime was committed — there are similarities with ALPR data.
Michael Soyfer, an attorney at the Institute for Justice, said at a Wednesday briefing that the Supreme Court emphasized that the “retrospective and indiscriminate” nature of the location history surveillance was particularly worrisome — adjectives which also apply to ALPR data.
The Chatrie ruling also bolsters the case against ALPRs because the court focused on what the police had access to globally in their database, according to Soyfer.
“The justices drilled down on what was in the database and not just what police happened to access at a point in time,” he said. “The court’s really emphasizing that it’s looking at the capabilities of the technology overall rather than just what police did with it.”
The Chatrie decision could have implications for cases involving reverse keyword searches, cell tower dumps and law enforcement purchase of commercial location data from brokers, Soyfer said.
A spokesperson for Flock Safety said in a statement that the court decision is not relevant to the company.
“The Supreme Court’s decision addresses geofence warrants for Google location history, which is categorically different from license plate recognition technology,” the statement said. “Google location history involves data from a person’s own mobile device and reveals continuous movements across both public and private places.”
“Flock’s ALPR technology, by contrast, captures point-in-time images of vehicles in public view.”
Courts have “repeatedly and uniformly” treated ALPR differently from technologies like cell site location information and mobile geolocation data, according to the statement.
“We do not believe this ruling undermines that settled precedent,” the statement said.
A side note in the Supreme Court opinion appears to differentiate the standard for what qualifies as a Fourth Amendment search based on whether the tracking occurs on “public roads,” according to the statement.
‘Indisputably private’
In the Chatrie case, the government argued that because the geofence searches involved the collection of data from short timeframes they did not warrant Fourth Amendment protections.
The high court sided with Chatrie, saying that the government is “wrong about the incapacity of short-term location information to reveal private matters.“
Even only a few hours worth of location history can reveal whether a citizen went to an “indisputably private” place such as the psychiatrist, an abortion clinic, an AIDS treatment center, a strip club, or a by-the-hour motel, according to the opinion.
“Location History enables police officers to focus on precisely those sites — to see, in a given time block, who shows up,” it said.
The fact that license plates are connected to law enforcement networks of personal data that reveal location, travel patterns and where people live make ALPR searches similar to cell phone location history searches in important ways, said Andrew Guthrie Ferguson, a law professor at George Washington University and the author of Your Data Will Be Used Against You.
“Modern ALPRs are just the connecting point to a much larger system of personally revealing information stored in police and connected public databases,” he said in an interview.
Those databases often contain not just ALPR data, but also documentation of individuals’ social media activity, surveillance video from thousands of public and private cameras, body cameras and drone video footage, gunshot audio detection sensor data and police dashboard cameras, Ferguson said.
Police also store granular information about people they are tracking in the databases, allowing them to build extraordinarily detailed dossiers.
“There are some differences with the nature of license plates that are after all designed for identification, but I think it is a mistake to think about ALPRs standing alone,” Ferguson said. “Chatrie certainly strengthens the Fourth Amendment case against the warrantless collection of ALPR data.”