PPSA Tells Eleventh Circuit that AI-Powered License Plate Tracking Violates the Fourth Amendment

United States v. Slaybaugh

Artificial intelligence has handed government surveillance a superpower the Founders never envisioned – the ability to quietly track millions of Americans, then rewind their movements later without a warrant.
 
In United States v. Slaybaugh, PPSA is urging the U.S. Court of Appeals for the Eleventh Circuit to draw a constitutional line around the warrantless use of automatic license plate reader (ALPR) databases. At stake is more than one defendant’s conviction. The court must decide whether rapidly evolving surveillance tools will stretch the Fourth Amendment beyond recognition for all Americans.
 
When Public Data Becomes Private Surveillance

Law enforcement offers a simple argument with surface appeal: License plates are visible on public roads, so collecting them invades no one’s privacy. In our brief, PPSA details how that simple argument collapses before the reality of modern surveillance.
 
This case is not about a single camera capturing a passing car. It is the government’s ability to aggregate billions of scans into a searchable chronicle of a person’s life. ALPR systems collect time-stamped and geolocated images of every passing vehicle, and store them indefinitely, allowing officers to reconstruct travel histories “with just the click of a button.” 
 
Far from snapping one static image of a license plate, ALPR systems have the power to tail everyone and anyone in a given city or county. That power transforms fleeting public observations into something fundamentally different – a digital dossier revealing where we sleep, worship, seek medical care, protest, or attend political meetings.
 
The U.S. Supreme Court recognized this danger in Carpenter v. United States (2018), holding that long-term location tracking can trigger Fourth Amendment protections even when a person’s movements occur in public. While Carpenter involved the extraction of a suspect’s geolocation history from a cellphone tower, ALPR surveillance raises the same constitutional concerns – but at a vastly higher scale.
 
The Myth of a Numerical “Safe Harbor”

One of the most significant errors PPSA identifies in the lower court’s ruling is the idea that surveillance becomes unconstitutional only after it collects a certain number of data points or weeks of tracking. The federal court treated the retrieval of 72 plate “reads” over three weeks as too limited to reveal the whole of one person’s movements. This take misreads Carpenter.
 
The danger lies not in how many time police officers choose to view images, but in the existence of the massive surveillance database itself.
 
Car “Fingerprints” and “Digital Time Travel”

PPSA told the court:

• “In 2019 alone, 1 billion license plate scans were collected, with 99.9 percent not actively related to any criminal investigation. The ALPR system that collected Slaybaugh’s information, Flock, works by creating a ‘vehicle fingerprint’ that includes much more than just a license plate number. Each passing vehicle’s ‘fingerprint’ includes its color, make, model, and distinctive features, like a political bumper sticker. Flock then provides advanced search and artificial intelligence functions that can be used to list locations a car has been captured, create lists of cars that have visited specific locations, and even track cars that are seen together.”

With such databases, officers can effectively travel back in time and retrace anyone’s movements long before suspicion arises. That retrospective power, PPSA demonstrates, far exceeds the general warrants and other abuses the Fourth Amendment was designed to restrain. In colonial America, the King’s agents lacked the ability to catalog every citizen’s movements. Modern technology has erased that practical limitation. Without constitutional safeguards, PPSA warns, the government can monitor entire populations’ travel histories and associations – whether political, romantic, or religious.
 
From License Plates to a Surveillance Ecosystem

ALPR systems are only one piece of a rapidly expanding surveillance architecture. PPSA warns that these tools increasingly integrate with other technologies – including AI analytics, neighborhood camera systems, and vast databases of commercial data sources holding personal information.
 
The concern is not simply about license plates. It is about the emergence of an interconnected surveillance ecosystem capable of mapping people’s lives in unprecedented detail.
 
The Solution Is Already in the Constitution

PPSA’s position is not anti-technology. We acknowledge that modern policing can benefit from advanced tools – so long as they operate within constitutional limits.
 
The solution is straightforward and familiar – requiring law enforcement to obtain a warrant supported by probable cause before querying historical ALPR data. That safeguard preserves investigative power while ensuring judicial oversight of government tracking.
 
The Future of Privacy
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The Eleventh Circuit’s decision may shape how courts treat digital tracking technologies far beyond license plate readers. As geofenced surveillance, AI drones, and integrated camera networks expand, the dangers of technology will only become more acute, and the constitutional principles at issue in Slaybaugh will only become more urgent.
 
Slaybaugh may well determine whether every time we get in our car, we are freely roaming public streets or becoming caught in a permanent dragnet.

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