Research · Court decisions
ALPR Case Law Library
Plain-English summaries of decisions on license plate readers and location surveillance. Each summary names the court, date and citation, says what the court held and what it didn't, and links to the opinion.
The library grows as we verify decisions. Each case is added only after we’ve read the opinion, verified the citation and checked its later history as far as public sources allow.
Cases
- U.S. Supreme CourtHeldUnited States v. Knotts460 U.S. 276 (1983) · decided 1983-03-02Using a radio beeper to follow a car on public roads was not a Fourth Amendment search. The Court reserved whether 'dragnet-type' surveillance might be treated differently.
- U.S. Supreme CourtHeldUnited States v. Jones565 U.S. 400 (2012) · decided 2012-01-23Attaching a GPS tracker to a vehicle and using it to monitor the vehicle's movements was a search. Five Justices, in concurrences, said longer-term GPS monitoring impinges on expectations of privacy.
- U.S. Supreme CourtHeldCarpenter v. United States585 U.S. 296 (2018); 138 S. Ct. 2206 · decided 2018-06-22Obtaining historical cell-site location records is a search, and the government generally needs a warrant. The Court called its decision 'a narrow one' and didn't address conventional tools such as security cameras.
- Massachusetts Supreme Judicial CourtFact-specificCommonwealth v. McCarthy484 Mass. 493 (2020) · decided 2020-04-16Four ALPR cameras at fixed points on two bridges did not amount to a search, but the court said widespread ALPR use could implicate constitutional protections.
- U.S. Court of Appeals for the Ninth CircuitFact-specificUnited States v. YangNo. 18-10341 (9th Cir. 2020) · decided 2020-05-04A driver of an overdue rental car lacked standing to challenge a warrantless search of a private ALPR database. A concurrence would have ruled the search didn't reveal the whole of his movements.
- U.S. Court of Appeals for the Fourth Circuit (en banc)HeldLeaders of a Beautiful Struggle v. Baltimore Police DepartmentNo. 20-1495 (4th Cir. 2021) (en banc) · decided 2021-06-24Accessing data from Baltimore's citywide aerial surveillance program was a search, and its warrantless operation violated the Fourth Amendment. Not an ALPR case, but a leading federal application of aggregation reasoning.
What every case summary includes
- The basics: case name, court, jurisdiction, decision date, citation or docket number
- The question the court was asked to decide
- The holding, quoted or closely paraphrased, kept separate from arguments and commentary
- What it means, and what it doesn’t: how far the ruling reaches, and where it doesn’t apply
- Later history: appeals, reversals or later cases that changed its weight
- A link to the opinion wherever it’s publicly available
Why one ruling doesn’t settle every case
A decision binds courts within its jurisdiction. A state supreme court ruling, for example, may be persuasive elsewhere but doesn’t control federal courts or other states. Facts matter too. Courts have looked at how many cameras were involved, how much location history was searched, and whether a warrant was obtained. Our summaries flag these limits so you don’t read more into a ruling than it holds.
For how courts approach the core question, see license plate readers and the Fourth Amendment.