What the Supreme Court's Chatrie Decision Means for ALPR Technology

The Supreme Court's recent decision in Chatrie v. United States concerning cell phone location data is one of the most significant Fourth Amendment decisions addressing digital privacy since Carpenter v. United States. The Court considered law enforcement’s access to Google's Location History—a technology that continuously records a person’s movements via their own cell phone, including movements inside homes and all other private places, creating a comprehensive record of where they have been.

Is Chatrie relevant to the ALPR industry?

This was not an ALPR case. Chatrie does not mention, much less directly address, automated license plate reader (ALPR) technology. However, Chatrie is relevant to the ALPR industry and to the legal questions surrounding it because the Court clearly articulates constitutional principles that reinforce the longstanding distinction between comprehensive digital tracking of people and technologies like ALPR that observe intermittent locations of vehicles on public roads.

The Constitutional Distinction

The Court emphasized multiple characteristics of Google's Location History data that, when combined, create what the Court described as a "virtual panopticon" of a person’s life that is far beyond the capabilities of even the most advanced and effective ALPR technologies:

• continuous data collection at all times, akin to an ankle monitor;
• extraordinary precision, even ascertaining elevation;
• access to comprehensive, lengthy historical records; and
• the ability to reveal movements into homes, doctors' offices, religious institutions, political meetings, and any other private place.
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The Court distinguished Location History and these characteristics from other types of technology used by law enforcement. Crucially, the Court expressly reinforced the settled principle that individuals do not have the same reasonable expectation of privacy while traveling on public roads as they do inside private spaces. It contrasted Google’s Location History with surveillance “confined to public roads” and referred separately to “public-movements-only technology.”

That distinction is especially significant for ALPR because it reflects and reinforces the fact that courts nationwide, including at the state and federal appellate levels, have consistently rejected Fourth Amendment challenges to the technology. They have uniformly distinguished ALPRs from the comprehensive cellphone tracking at issue in the Carpenter decision. Courts have recognized that ALPR systems are limited to discrete observations of vehicles on public roadways, captured only where ALPRs exist. And, unlike Google Location History or cell site data, ALPR data cannot continuously monitor a person's movements, reconstruct virtually every aspect of daily life, or reveal activity inside private spaces. Chatrie unambiguously reinforces that reasoning. 

Safeguards Support Responsible Use

Chatrie also underscores an important point: technologies with legitimate public-safety value should operate within meaningful legal safeguards. That is already true for Flock’s ALPR systems. Across the country, legislatures and local governments have adopted rules governing retention periods, permissible uses, auditing, access controls, transparency, and penalties for misuse. Virginia, for example, limits retention of ALPR data to 21 days—another distinction from the effectively unlimited historical records at issue in Chatrie.

Flock itself has built, and continuously enhances, privacy protections directly into its ALPR system, including role-based access controls, audit logs, and user accountability. Together, these legal and technical safeguards reflect an important principle: privacy is protected not only by constitutional doctrine, but also through democratic governance.

The Constitutionality of ALPR Systems

In short, Chatrie recognizes that cell phone technologies capable of creating comprehensive digital records of people’s private lives raise legitimate constitutional concerns. But the Court did not address ALPR technology. It did not disturb the extensive, uniform body of precedent distinguishing fixed public-road cameras from comprehensive cellphone tracking. Instead, the Court explained why Google's Location History was constitutionally distinct from technologies such as ALPR that do not and cannot achieve anywhere near the level of personal tracking at issue in Chatrie. In so doing, the Court reaffirmed the very distinctions that have long supported the constitutionality of ALPR systems: discrete observations of vehicles in public, not continuous surveillance of people everywhere they go.  

For ALPR systems that observe vehicles at fixed points on public roads, the principles announced in Chatrie reinforce the lawfulness of this critical technology used by law enforcement agencies nationwide to keep their communities safe.

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Sasun Bughdaryan on Unsplash
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