License plates are, by design, meant to be visible. That simple fact is the legal hook that has let ALPR surveillance expand for two decades with relatively little federal oversight. This article lays out where the law actually stands — not where advocates wish it stood — so you know what protections exist and where the open fights are.

The starting point: plates are public

Courts have long held that a license plate displayed on a public road carries no reasonable expectation of privacy. A single officer writing down your plate number, or a toll camera reading it once, has never been treated as a search under the Fourth Amendment. That baseline hasn’t changed.

What has changed is scale. The legal question courts are now wrestling with isn’t “can they read one plate,” it’s “does storing millions of reads over months turn passive observation into surveillance the Constitution should regulate.”

Carpenter v. United States and the “mosaic theory”

In Carpenter v. United States (2018), the Supreme Court ruled that police needed a warrant to obtain seven days of a person’s cell-site location records, declining to apply the older “third-party doctrine” (the idea that once you share data with a company, you lose any privacy interest in it) to detailed location histories. The Court reasoned that comprehensive location tracking reveals intimate details of a person’s life — associations, habits, and movements — that a single data point never could.

That reasoning, sometimes called the “mosaic theory,” is the basis for arguments that large ALPR networks should also require a warrant once enough cameras accumulate enough history on a single vehicle. The Supreme Court has not ruled directly on ALPR, so lower courts have had to work this out case by case, with mixed results:

  • In Commonwealth v. McCarthy (2020), the Massachusetts Supreme Judicial Court found that widespread ALPR use can implicate a Fourth Amendment privacy interest in a person’s overall movements — but ruled that the limited camera network at issue in that case didn’t rise to that level.
  • In Schmidt v. City of Norfolk, plaintiffs backed by the Institute for Justice argued that Norfolk, Virginia’s roughly 176-camera network was dense enough that querying it without a warrant amounted to a search. A judge granted summary judgment for the city in January 2026; the case is on appeal.
  • Federal courts have generally been more reluctant than state courts to extend Carpenter to ALPR queries, meaning your protection can depend heavily on which state and which court you’re in.

In short: the law is unsettled and actively being litigated, state by state and circuit by circuit.

What state law adds (or doesn’t)

The Fourth Amendment sets a floor, not a ceiling. States are free to pass stronger protections, and a handful have: retention limits, warrant requirements for certain queries, and restrictions on sharing data with out-of-state or federal agencies. Most states haven’t passed ALPR-specific legislation at all, which means the rules governing your local police department’s ALPR program are often whatever that department’s internal policy says — not a legislature’s. See our state-by-state legal overview to check where your state falls, and our piece on ALPR data retention policies for how long agencies typically keep this data.

What rights actually look like in practice

Because ALPR sits in a legal gray zone, the practical protections available to you are mostly procedural, not constitutional:

  • Public records requests. In most states, you can file a public records request to see your local department’s ALPR policy, retention schedule, and — sometimes — sharing agreements with other agencies.
  • Local policy fights. City councils and county boards, not courts, are where most ALPR rules actually get written. The ACLU’s 2013 nationwide survey, built from roughly 600 public records requests, remains one of the most cited baselines for how loosely most departments were regulating this data.
  • State legislation. A growing number of states introduce ALPR bills each year, though the Brennan Center notes that most fail to pass, and the ones that do vary widely in strength.

Should you expect to opt out?

Not really — at least not in the sense of removing your car from these systems. We cover the limited practical options in Can you opt out of license plate reader surveillance?.

The bottom line

Your plate has always been public. What’s new is the permanence and searchability of the record that gets built from it. Courts are still deciding whether that shift matters constitutionally, and in the meantime, your strongest lever is usually local: knowing what your own city’s cameras capture, and pushing for retention and sharing limits at the city council level rather than waiting on a Supreme Court ruling. Start by checking what’s been mapped near you on the FlockScanner map.