The Chatrie Decision and ALPR

Yesterday, we discussed the amicus brief in Schmidt v. Norfolk and referenced the Supreme Court’s decision in Chatrie, which dropped at the same time. This article will take a deeper look at Chatrie, and tell you why Flock’s next blog post will be wrong about what the decision says.

Flock, and other pro-mass surveillance parties, will present Chatrie as reaffirming the one cited line from Knotts. I don’t doubt that they have a blog post in the making highlighting this paragraph from Chatrie:

… another feature of Knotts makes it inapt here: that the surveillance there was confined to public roads. That fact was crucial to the Court’s decision: “A person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy,” Knotts explained, because the car is always “in plain view.” 460 U. S., at 281. By contrast, the movements that Location History reveals are not limited to public streets. Recall what Carpenter observed: A “cell phone faithfully follows its owner beyond public thoroughfares and into private residences, doctor’s offices, [and] political headquarters.”

This line of reasoning is somewhat similar to the District Court’s finding in Schmidt v. Norfolk, based on Carpenter, and it’s pretty much what informed Flock’s oft-repeated “we don’t track people” line.

The argument by itself is persuasive enough, but it can only work if you disregard the rest of the Chatrie opinion as well as Beautiful Struggle.

As yesterday’s post also conceded, Knotts is not wrong, per se. Nobody is making the argument that a single observation of a vehicle on a public road does not pass constitutional muster. But that’s not what the search in Chatrie is about — in Chatrie, nobody argues that the observation and collection of the location history data (by Google) was unconstitutional. The Supreme Court never asks, let alone answers, that question. Both Chatrie and Carpenter found a search occurred when the government accessed a pre-compiled, retrospective database containing location history data.

Both Google and Flock are private companies. A private company collecting a user’s location or taking a picture of a vehicle on a public street is not by definition unconstitutional, nor is aggregating that information in a national database. To be clear: I believe Flock deployments generally aren’t legal, but my objections to the cameras themselves are largely statutory, not constitutional.

In Carpenter, the court examined the government’s access to a historical database: the phone company may have collected years worth of data, but the government’s act of looking at 7 days of CSLI records triggered the Fourth Amendment. In Chatrie, the court works through the reasons why location history is private and not voluntarily disclosed (in any real sense), before writing: “we hold that police officers invade a cell-phone user’s reasonable expectation of privacy when they access his Location History.” (emphasis added)

It then restates the same holding: “When the government ‘accesses historical cell phone’ location information—Location History as much as CSLI—it ‘conducts a search under the Fourth Amendment.’”

Access, not collection. Even if the collection — the observation and recording of a vehicle traveling on a public street — would be legal under Knotts, it’s the government’s access of the retrospective database that creates the search under both Carpenter and Chatrie.

That distinction holds even if we were to assume that Flock’s retrospective database contains only observations permissible under Knotts — which is something we know not to be true, because deployments on private property exist, but is a fact that plaintiffs in Schmidt may have conceded.

But, for the sake of argument, let’s say when the Supreme Court wrote about “access” they really meant to include something about the location where the data was collected.

Beautiful Struggle^[1] held that the compilation of retrospective data itself “is enough to yield ‘a wealth of detail,’ greater than the sum of the individual trips”, and “because people’s movements are so unique and habitual, it is almost always possible to identify people by observing even just a few points of their location history.” The court in Beautiful Struggle agreed you can infer a lot of information from a historical database; those inferences fall outside of what is exposed to the public and would be observable under Knotts.

The Fourth Circuit did not treat that conclusion as its own intuition; it drew the principle from the Supreme Court itself, quoting Justice Sotomayor’s observation in Jones that people do not expect “that their movements will be recorded and aggregated in a manner that enables the government to ascertain” the details of their private lives.^[2]

It’s also an argument plaintiffs made in Schmidt, and the one Flock attempted to rebut on a redacted page with (only) the heading “The Flock Camera Data Does Not Enable an Individual to ‘Infer’”. But the District Court found that the data does allow inference of certain aspects of life. The District Court also found that the inference was not enough to trigger a search, but Chatrie now rejects that quantitative test:

… this Court has never understood Fourth Amendment protections as kicking in only once an intrusion “goes too far,” Where the Fourth Amendment applies, it applies regardless of “the quality or quantity of information” the government obtains. That approach makes all the more sense when, as with Location History, law enforcement officials can select the time-limited set of materials they want from an all-encompassing database.

The record in Schmidt shows that capacity to infer exists: plaintiffs’ expert found Flock captured 78.7% of modeled routes, most of them reconstructable because they pass two or more cameras — exactly the ability to rebuild a person’s movements that, under Beautiful Struggle, makes those inferences possible.

Flock’s headline takeaway will be that the 1983 Knotts case about tracking a beeper in a car still stands. The Fourth Circuit should conclude, as they did in 2021 in Beautiful Struggle, and as the Supreme Court did yesterday in Chatrie, that the correct answer to that is: “so what?”

Flock’s best argument has always been that all it does is photograph the back of a car. But under Chatrie, data collection is not the search. The search happens when the government delves into the database built from the photographs — and into everything it lets them deduce.

Forty years ago, Knotts was about watching a car’s location on a road; now, Chatrie and Beautiful Struggle are about accessing location histories. The fight is moving into the 21^st century: from cars and cameras to databases and computer analysis. That’s the seismic wave Alito fears. Flock should too.