Should the Use of Automated License Plate Readers Constitute a Search After Carpenter v. United States?


Are our privacy interests implicated when police keep records of each and every time our cars are spotted by automated license plate readers? For many years, police have used automated license plate readers (ALPRs) to, among other things, “determine whether a vehicle was at the scene of a crime, to identify travel patterns, and even to discover vehicles that may be associated with each other.” These automated license plate readers are high-speed cameras that can be either stationary, e.g. mounted on street poles, highway overpasses, and the like, or mobile, such as when they are mounted on police cars. ALPRs automatically capture snapshots of all license plates that come within their line of sight, recording simultaneously the location, date, and time of the photograph. All the data collected—at times even including images of cars and passengers—is then uploaded to databases that store the information for extended periods of time, sometimes as long as five years. The data can also be analyzed instantaneously before being stored, such as to determine if the vehicle appears on a “hot list.” These “hot lists” catalogue a series of license plates associated with stolen vehicles or vehicles suspected of involvement in a crime. When an automated license plate reader scans any license plate appearing on a “hot list,” the police are notified.

At first glance, automated license plate readers may not seem to pose a great threat to privacy interests. After all, they only capture license plate data in individual snapshots. They mark one moment in time, and that seems harmless enough. However, in the aggregate, the pings associated with one license plate can paint a detailed picture of that vehicle and its driver’s movements. They can even reveal intimate details about an individual’s life as a whole. The stored license plate reader data enables police to make highly accurate estimations regarding individuals’ homes, places of work, favorite hangout spots, etc. Police can then infer where an individual will go based on where they have been. What makes this even more troublesome is that drivers must display a license plate, allowing automated license plate readers to track the movements of everyone in the vicinity, not just those under suspicion of having committed a crime.

Police departments and the government have justified the use of automated license plate readers by stating that the practice occurs in public and is simply a more efficient version of officers recording license plate numbers by hand and entering them into a database. They rely on the general precedent that there is no reasonable expectation of privacy on public thoroughfares. Nevertheless, while the information collected on one occasion is readily available to the public, and a police officer could record it by hand, the accumulation of data points over an extended period of time for an enormous number of drivers is not something the public or the police could easily track. Without automated license plate readers, police officers would be forced to choose what vehicles to monitor. Automated license plate readers, therefore, eliminate the practical limitations on the collection of license plate data that once protected an individual’s privacy.

Before the development of automated license plate readers and other new technologies, “our ability to blend into a crowd [served] as sufficient protection” against government invasion of our privacy. The whole of our movements could not be detected. But now, in most communities, we are no longer anonymous individuals in a crowd. Mass data collection methods, such as automated license plate readers, eliminate our anonymity, and the law must adapt to this changing reality. Given the intimate details that automated license plate readers can reveal, we should have a reasonable expectation of privacy with regard to the aggregated information they collect. Carpenter v. United States is in line with this assertion.

In Carpenter, the Supreme Court examined whether an individual had a reasonable expectation of privacy with regard to cell-site location information cataloguing his movements over a 127-day period. The Court ultimately held that the government’s acquisition of Carpenter’s cell-site location information constituted a search under the Fourth Amendment and that a search warrant is required to obtain this information. In coming to this conclusion, the Court read its prior decisions as establishing a right to privacy in the whole of an individual’s movements. The Court’s holding, many commentators believe, calls into question a wide variety of mass data collection methods.

This Note will analyze whether the use of information collected by automated license plate readers should be considered a search under the Fourth Amendment in light of the Court’s recent identification of a right to privacy in the whole of an individual’s movements. Given that automated license plate readers can reveal so many intimate details about our lives, is there a reasonable expectation of privacy with regard to the use of this information? Should a query of the aggregated data stored for each license plate be considered a search under the Fourth Amendment? Are there sufficient parallels between cell-site location information and automated license plate reader data so that a conclusion similar to that in Carpenter will be reached regarding automated license plate readers? This Note will argue that the answer to all of these questions is yes.

The Fourth Amendment is meant to protect the public from the overreach of police surveillance and arbitrary power. The government’s ability to view pings from automated license plate data collected over an extended period of time, with no detectable check on this power, signifies an overreach of police surveillance. Further, there are identifiable parallels between the collection of cell-site location information and automated license plate reader data, which suggests queries of automated license plate reader data should similarly require a search warrant. Both types of surveillance eliminate the practical limitations police previously faced, which protected individuals against invasions of their privacy. Moreover, automated license plate reader data, while not as constant as cell-site location information, allows the police to gain a thorough understanding of an individual’s familial, political, professional, religious, and even sexual associations. Finally, automated license plate reader data, like cell-site location information, is retroactive and involves the collection of information on all individuals and not just those accused of crimes. This means police need not know ahead of time who the target of the investigation will be; everyone is surveilled.

For these reasons, a database query for information on a particular license plate, and therefore the individual driving that vehicle, should be considered a search under the Fourth Amendment. However, a search warrant should not be required for the collection of automated license plate reader location data. Even though the existence of these databases can seem troubling, in the interest of not harming law enforcement efforts, police should be permitted to collect license plate information without needing a search warrant. Similarly, there should be an exception to the search warrant requirement for checking vehicles against a “hot list,” as this should not be considered a search under the Fourth Amendment. Checking any one license plate at a particular moment would not violate the individual’s reasonable expectation of privacy. It is instead the aggregation of license plate data and the inferences that can be made from querying license plate databases that are particularly troubling and therefore should be regulated.

Part I of this Note provides additional details regarding the use and implications of automated license plate readers and their data. It also surveys Fourth Amendment jurisprudence leading up to the landmark decision Carpenter v. United States. Part II discusses the consequences of Carpenter with regard to automated license plate readers and advocates for requiring a search warrant in order to query a database containing automated license plate reader data.

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