Judge Says Warrantless Flock Search Violated Driver’s Fourth Amendment Rights

Today, there’s yet more evidence that the tide is turning against Flock, an automated license plate reader (ALPR) system in pervasive use around the country. Calling it “indiscriminate mass surveillance,” a federal court in Oklahoma granted a woman’s motion to suppress evidence found in her car after a search that was conducted based on information obtained through Flock.

The court’s scathing and beautiful takedown of warrantless Flock searches is something to behold.

“Think about it this way. We might reasonably expect our friends and family to tell us something like: ‘Hey, I saw you out driving by the store last week,'” writes Judge Sara E. Hill of the U.S. District Court for the District of Oklahoma. “But we do not expect people we know—let alone strangers, and especially not law enforcement—to randomly approach us to say: ‘Hey, I have been following your car for the last 30 days, and here is a detailed log of every place your vehicle has been with supporting photographic evidence. I am also going to share this information with law enforcement throughout the country so they know your whereabouts, too.'”

“Freedom from persistent, dragnet-style surveillance while in public…is a reasonable expectation,” adds Hill, rejecting previous court holdings that law enforcement using automated license plate reader systems are not “searches” for Fourth Amendment purposes.

The 4th Amendment Quandary

The Flock system—and similar programs—capture images of people’s cars and store these images along with the time and location they were captured and details about the car’s make, model, and various other features. Authorities can later query the system about specific vehicles (using license plate number or description) or to search for all vehicles that drove in a given area at a given time.

High-profile instances of cops using Flock for stalking purposes have made news. But the bigger issue is how these tools are being used in legitimate cases: without warrants. And often without reasonable suspicion.

The protocol that has emerged around ALPR systems does not involve cops presenting probable cause and obtaining a warrant before conducting a search.

This protocol seems to be in direct opposition to the Fourth Amendment. But at least one federal court has already given this its blessing. In September, the U.S. District Court for the Central District of California held that querying the Flock database is not a “search” for Fourth Amendment purposes. According to Judge Virginia A. Phillips, no probable cause or particularized warrant is required before cops conduct a search.

It’s reassuring to see the U.S. District Court for the District of Oklahoma come to a very different conclusion than the California court did.

The Traffic Stop

The current case concerns the Tulsa County Sheriff’s Office and Deputy Sheriff Freddie Alaniz. After an ALPR system on his car noticed a car with a California license plate drive by on the highway, Alaniz started following the car and also searched Flock for its license plate number.

In the spot where he could list the reasons for the query, he wrote “traffic violation” and “investigation,” even though “at the time of those queries, all Alaniz knew was that the vehicle had a California license plate,” as Hill explains in the court’s decision. The Flock query revealed that the car had traveled from Oklahoma toward somewhere near the California/Arizona border before heading back east.

Alleging a failure to signal lane changes sufficiently early and driving too close to a car in front of it, Alaniz eventually pulled over the driver, Melisa Kyle, and asked her about her recent travel. She explained that she had been visiting a cousin and gave some other details about her trip and why she had about a half dozen suitcases in her backseat.

After giving her a warning and returning her license, Alaniz told Kyle that “people who do very short trips to California and come right back are usually transporting large amounts of drugs” and asked to search her car. She said no.

Alaniz then detained Kyle, called for backup, and had his dog sniff her car. They allegedly found meth, and Kyle was charged with possession with intent to distribute.

Kyle moved to suppress the search evidence, asserting that the stop was unjustified, that Alaniz extending the stop beyond the initial conversation was unjustified, and that Alaniz’s search of the license plate surveillance system was unlawful.

“Based on the Court’s review of the record, Alaniz had an objectively reasonable basis to stop the Mazda for following the car in front of it too closely,” writes Hill in the court’s decision.

Suspicious Travel?

But Alaniz did not have reasonable basis for extending the traffic stop after returning Kyle’s license, Hill decided:

Kyle’s short trip to California might not have been something Alaniz would have personally done. But Kyle had a reasonable explanation for the short turnaround—that the drive was as fulfilling as seeing the people she visited. As the Tenth Circuit has recognized, “[t]here is nothing criminal about traveling by car to view scenery.”

Hill similarly rejected the government’s assertions that other elements of Kyle’s road trip and recollections of it justified the search.

The judge’s total repudiation of the cop’s rationale here is worth sharing, because it highlights the way that all sorts of reasonable and mundane things can be regarded as “suspicious” by police who are motivated to find things suspicious—and wholeheartedly rejects this:

In the Court’s view, Alaniz did not have enough information to reasonably believe that Kyle was engaged in unlawful conduct. The factors that the government relies upon are the same type of circumstances that everyday Americans encounter on long road trips for many legitimate reasons. Many of us drive longer than we want to get to a desired destination, or to no destination at all other than the road and sights ahead. Many of us lose track of what exact day of the week it is when we are traveling, even if it is for just a moment. Many of us travel for myriad reasons (some better than others), cross state lines, pack too much, buy too much, smoke cigarettes, and rent cars. And many of us even get a bit nervous when talking to law enforcement.

A ‘Constitutionally Problematic’ Search

This brings us to the Flock search. The government argued that there was nothing unconstitutional about it because the data that make up Flock databases is obtained on public roadways and people like Kyle do not have a reasonable expectation of privacy on public roadways.

This is a common assertion. “Based on the Court’s research, it appears that nearly every court examining the issue to date has determined that [atuomated licsene plate reader} technology use is not a search under the Fourth Amendment because people have no reasonable expectation of privacy in their movements on public streets,” notes Hill. “Indeed, several other Oklahoma federal courts have decided the issue this way.”

Hill gloriously disagrees.

While it’s true that “people, in at least a broad sense, do not have a reasonable expectation of privacy in their movements on a public roadway,” the Flock system goes beyond simply seeing someone on a road.

“This is a type of indiscriminate mass surveillance,” she writes. “It is not targeted on a single individual….It is a tool that collects information about all vehicles that pass by any network-connected camera at all times, and it serves up the information to law enforcement on demand.”

In Kyle’s case, “Alaniz had access to an entire month’s worth of location data tied to the license plate on Kyle’s car, including more than fifty sightings across multiple states,” Hill points out. “Alaniz and other officers using these systems have access to a continuously updated location history for all vehicles caught on ALPR cameras within the network.”

A right not to be subjected to “dragnet-style surveillance while in public…is the same
expectation of privacy that the Supreme Court has continued to recognize,” she adds, citing as one example Chatrie v. United States (2026).

In Chatrie, the Court held that geofence warrants—in which cops demand data on all phones within a given location at a given time—do count as searches that trigger due process protections.

“Cell phones also move in public places where people can see you in plain view,” noted Hill. “But it becomes constitutionally problematic when law enforcement can indiscriminately and passively catalog your whereabouts over an extended period of time and then use that information for any purpose whenever convenient.”

Evidence Suppressed

With Kyle, “the only reason Alaniz conducted that search was because he saw her license plate was from California,” notes Hill. “That search was not supported by probable cause, and it was done without a warrant in violation of Kyle’s Fourth Amendment rights.”

Because of this, “all evidence obtained after Alaniz initiated the [license plate reader] search must be suppressed as fruit of the poisonous tree,” she ruled.

“This decision is an important next step from the Supreme Court’s pivotal recognition this year in Chatrie v. U.S. that Americans have a reasonable expectation of privacy in the whole of their physical movements,” said Tom Bowman of the Center for Democracy and Technology in an emailed statement.

“Previously, courts generally did not require a warrant for police to search the information collected by license readers, despite the fact that the technology allows easy reconstruction of Americans’ movements over time,” he noted. “License plate readers enable indiscriminate mass surveillance, and as other courts should, Judge Hill’s decision brings constitutional protections in line with that reality.”

This is the second federal court decision in a little over a week to suggest that driver surveillance systems can go too far.

On September 28, the jury on a federal case out of San Antonio held that a Bexar County, Texas, policing program involving surveillance cameras that recorded license plates and pretextual traffic stops was unconstitutional.

“This is a huge win, and not just for [the plaintiff in this case],” said Institute for Justice Attorney Christie Hebert in response to the Bexar County verdict. “Motorists across this country are being watched by local, state and federal agents, flagged by AI-powered cameras, and then pulled over for a bogus offense that exists only as a cover story for an interrogation and a search. The Fourth Amendment does not permit this.”

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