Judge Rules Warrantless Flock Search Violated Driver’s Fourth Amendment Protections

Today, there’s yet more evidence that the tide is turning against Flock, a widely used automated license plate reader (ALPR) network across the country. Labeling it “indiscriminate mass surveillance,” a federal court in Oklahoma granted a woman’s motion to suppress evidence found in her vehicle after a search based on data obtained through Flock.

The court delivered a sharp, forceful critique of warrantless Flock searches, a ruling that stands out for its clarity.

“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 come up to us and say: ‘Hey, I have been tailing 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 across the country so they know where you are, too.'”

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“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 Fourth Amendment Dilemma

The Flock network—and similar programs—capture images of vehicles and retain these images along with the time and location they were captured, plus details about the car’s make, model, and other features. Authorities can later query the system about specific vehicles (by plate number or description) or search for all vehicles that traveled in a given area at a specific time.

High-profile uses of Flock by law enforcement for stalking-like purposes have attracted attention. Yet the bigger concern is how these tools are used in legitimate contexts: without warrants. And often without reasonable suspicion.

The protocol that has emerged around ALPR systems does not require officers to show probable cause and obtain a warrant before conducting a search.

This protocol appears to clash with the Fourth Amendment. But at least one federal court has already blessed it. 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 officers conduct a search.

It is reassuring to see the U.S. District Court for the District of Oklahoma reach a markedly different conclusion from the California court.

The Traffic Stop

The case at hand involves the Tulsa County Sheriff’s Office and Deputy Freddie Alaniz. After an ALPR system on his vehicle flagged a car with a California plate, Alaniz began tailing the vehicle and also searched Flock for its plate number.

In the field where he listed the grounds for the inquiry, he wrote “traffic violation” and “investigation,” even though “at the time of those queries, all Alaniz knew was that the vehicle carried a California plate,” as Hill explains in the ruling. The Flock query showed that the car had traveled from Oklahoma toward the California/Arizona border before heading back east.

Accusing the driver, Melisa Kyle, of failing to signal lane changes early enough and following too closely, Alaniz eventually stopped her and questioned her about her recent travel. She explained she had been visiting a cousin and provided some other details about the trip and why she had roughly half a dozen suitcases in the back seat.

After issuing a warning and returning her license, Alaniz told Kyle that “people who make very short trips to California and return shortly thereafter are typically transporting large quantities of drugs” and requested permission to search her car. She refused.

Alaniz then detained Kyle, summoned backup, and had his dog perform a sniff of her vehicle. It is alleged that methamphetamine was found, and Kyle was charged with possession with intent to distribute.

Kyle moved to suppress the evidence from the search, arguing that the stop was unjustified, that the extension of the stop beyond the initial conversation was unwarranted, 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 vehicle in front of it too closely,” writes Hill in the court’s decision.

Questionable Travel?

But Alaniz did not have a reasonable basis to extend the traffic stop after Kyle’s license was returned, Hill concluded:

Kyle’s short trip to California might not have been something Alaniz would have personally undertaken. But Kyle offered a reasonable explanation for the brief turnaround—that the trip served as a chance to visit family as well as to see the people she visited. As the Tenth Circuit has acknowledged, “[t]here is nothing criminal about driving to view scenery.”

Hill likewise rejected the government’s arguments that other aspects of Kyle’s road trip and her recollections substantiated the search.

The judge’s complete rejection of the officer’s rationale here is notable because it underscores how many ordinary, legitimate circumstances on long road trips can be misread as “suspicious” by investigators—who then accept this reading without proper justification:

In the Court’s view, Alaniz did not have enough information to reasonably believe that Kyle was engaged in unlawful conduct. The factors the government cites are the same kinds of circumstances that everyday Americans encounter on lengthy road trips for legitimate reasons. Many of us drive longer than we would like to reach a destination, or simply for the experience of the road and sights ahead. Many of us lose track of the exact day of the week while traveling, even if only briefly. We travel for countless reasons, cross state lines, pack too much, buy more than we need, smoke, and rent cars. And many of us even feel a bit uneasy when talking to law enforcement.

A ‘Constitutionally Troubling’ Search

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

This is a common claim. “Based on the Court’s research, it appears that nearly every court addressing the issue to date has found that automated license plate reader technology use is not a Fourth Amendment ‘search’ because people lack a 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 firmly disagrees.

While it is true that “people, in a broad sense, do not have a reasonable expectation of privacy in their movements on a public roadway,” the Flock system goes beyond merely observing someone on a road.

“This is a form of indiscriminate mass surveillance,” she writes. “It is not aimed at a single individual…It is a tool that collects information about every vehicle that passes by any network-connected camera at all times, and it provides that information to law enforcement on demand.”

In Kyle’s case, “Alaniz had access to a full month’s worth of location data tied to Kyle’s license plate, including more than fifty sightings across several states,” Hill notes. “Officers using these systems have access to a continuously updated location history for all vehicles captured by ALPR cameras within the network.”

A right to be free from “dragnet-style surveillance while in public” aligns with the privacy expectations recognized by the Supreme Court, she adds, citing as an example Chatrie v. United States (2026).

In Chatrie, the Court held that geofence warrants—where police demand data on all phones within a defined location at a specific time—count as searches that trigger due process protections.

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

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 conducted 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 marks an important next step beyond the Supreme Court’s pivotal recognition this year in Chatrie v. U.S. that Americans have a reasonable expectation of privacy in the totality 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 marks the second federal court ruling in a little over a week suggesting that driver-surveillance technologies can go too far.

Earlier, on September 28, a San Antonio jury found that a Bexar County, Texas policing program involving cameras that recorded license plates and pretextual traffic stops violated the Constitution.

“This is a major victory, and not just for the plaintiff in this case,” said Institute for Justice Attorney Christie Hebert in response to the verdict. “Motorists across the U.S. are being monitored by local, state, and federal agents, flagged by AI-powered cameras, and then stopped for a sham offense used to justify interrogation and a search. The Fourth Amendment does not permit this.”

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