Carpenter v. United States is cited by guests on The Bob Zadek Show as one of two recent Supreme Court decisions anchoring what legal scholars call the mosaic theory — the proposition that collecting individual data points may be lawful while assembling those points into a picture becomes a Fourth Amendment search. The case is discussed in three episodes, once in a 2022 conversation about anonymity and twice in conversations about automated license plate readers.
The 2017 holding as described by Jonathan Hofer
In two episodes, Jonathan Hofer places Carpenter in a sequence alongside United States v. Jones (2012). He notes that Gorsuch was on the bench by 2017, and describes the facts as revolving around what he believes was a bank robbery. In that case, he says, the government used cell phone tower data to track the cell phones of the suspects. The Supreme Court, in his account, said the government could not do that, and further held that it could not retrace the steps of the suspect using historical data exceeding 12 days The Mass Surveillance nobody is talking about (2022).
Hofer contrasts the two decisions. Jones involved a GPS tracker placed on a suspect’s car in the greater DC area; police said the man was dealing drugs, the car traveled out of the jurisdiction, and although the warrants expired, tracking continued. The Supreme Court unanimously held that the government cannot GPS track a vehicle. In Carpenter, by contrast, the data at issue was cell phone tower data rather than a device physically attached to a vehicle A PSA on ALPRs (2022).
Before reaching Carpenter’s application, Hofer sets out the mosaic theory itself: even if collecting individual data points is legal, once a picture is created with those points, it becomes a Fourth Amendment search A PSA on ALPRs (2022).
Extension to ALPRs
Hofer’s central argument is that combining Jones and Carpenter yields a serious argument that license plate readers as practiced in California and throughout the nation are unconstitutional. ALPR location data, he concedes, is not technically GPS and does not use a satellite, but he characterizes it as an effective substitute for GPS data, logging latitude and longitude over the internet and creating a picture of a person’s life that can be used with historical data to track whereabouts The Mass Surveillance nobody is talking about (2022).
He states that no ALPR case has been before the Supreme Court and that nothing is coming up on which the Court will rule on general ALPR use. Lower courts, however, have endorsed the mosaic theory. He names Commonwealth v. McCarthy, from the Massachusetts State Supreme Court, where a woman was spotted crossing a bridge where an ALPR was installed, and another case in a Texas court that he believes may have been a Court of Appeals but whose district he is not sure of. In both, the courts ruled in favor of the state, reasoning that a single camera and, in Texas, a single scan did not yield enough data to form a mosaic A PSA on ALPRs (2022).
Hofer disputes that factual premise in the California context. He cites Piedmont, a city of less than two square miles with almost 40 cameras, and Los Angeles with 500 cameras. He notes that a man in San Leandro made a public records request and found his car had been scanned about 100 times. On his contention, that constitutes a mosaic search and would require a warrant The Mass Surveillance nobody is talking about (2022).
Privacy legislation
Jeff Kosseff invokes Carpenter in a 2022 episode on anonymity, though cautiously. Addressing Bob Zadek’s question about whether facial recognition differs from a private actor simply recognizing someone in public, Kosseff agrees from a Fourth Amendment perspective but says that “although sort of post-Carpenter, I’m not willing to totally” — the excerpt breaks off there — the outcome is not fully settled The United States of Anonymous (2022). He does not describe the holding of Carpenter in that episode and does not state what it turned on.
Kosseff’s larger point is that data in the public view is hard to control when the government uses what a person has publicly posted, and that privacy law rather than the First or Fourth Amendment is the better instrument. He notes that California has passed two privacy laws giving people the ability to access data stored about them and to request its deletion, which he calls a positive step but not a panacea, partly because he does not know every data broker holding information about him. He calls for rules specifying how facial recognition can and cannot be used, and for a national privacy law The United States of Anonymous (2022).
Across episodes: the mosaic argument
The mosaic theory and Carpenter appear in the two ALPR episodes with substantially identical wording, both attributed to Jonathan Hofer: the explanation of the theory, the Jones and Carpenter sequence, the 12-day threshold, the Commonwealth v. McCarthy reference, and the Piedmont and Los Angeles camera counts recur across the two transcripts. In the earlier conversation on mass surveillance, the material is presented as part of a broader discussion of ALPR data storage and misuse; in the later episode titled as a PSA on ALPRs, the same passage appears under a heading on mosaic theory and legal precedents, leading into private collection and civil litigation rather than into the discussion of department cybersecurity, sanctuary city laws and data-sharing arrangements that precedes it in the earlier episode. Jeff Kosseff’s treatment in the anonymity episode is separate and considerably more tentative: he references Carpenter only to say the post-Carpenter landscape is not fully known, and routes the facial recognition problem toward legislation rather than constitutional doctrine.
What the sources do not cover
The excerpts do not reproduce the Court’s reasoning in Carpenter, identify the Justice who wrote the opinion, or state which provision of the Constitution the decision turned on. They do not give the case’s docket number, the date of decision beyond the year 2017, or the identity of the petitioner. United States v. Jones is likewise reported only at the level of year, author, and facts as the guest recalls them. California’s two privacy laws are described by function only, without names, and the Texas case endorsing the mosaic theory is left unidentified by court and district.