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1 [1] (July 21, 2025)

handle is hein.crs/agehoiih0001 and id is 1 raw text is: Congressional Research Service lnforrning the legislative debate since 1914 July 21, 2025 Automated License Plate Readers: Background and Legal Issues Automated license plate readers (ALPRs) are camera systems that capture the license plate data of vehicles, along with related information. They are generally available in fixed and mobile formats. Fixed ALPR systems are mounted in specific locations, often using existing infrastructure such as light poles, traffic lights, buildings, or bridges. Mobile ALPR systems are frequently mounted on police vehicles or privately contracted vehicles. Although details vary by system and jurisdiction, information obtained from ALPR systems may be included in certain databases-whether maintained by public or private entities-that are accessible or searchable by law enforcement. Law enforcement agencies use ALPRs for a variety of proactive and reactive policing purposes, including to gather intelligence and evidence, help identify potential suspects, and facilitate crime scene analysis. Law enforcement use of ALPRs raises a range of questions for policymakers and the public. For instance, one consideration is how ALPR use may, while aiding criminal investigations, potentially infringe upon individuals' privacy and civil liberties-in particular, Fourth Amendment protections from unreasonable searches and seizures. In general, courts have found that mere observation of an object in plain view does not implicate the Fourth Amendment, which suggests that law enforcement's initial reading of a license plate using an ALPR is ordinarily not a Fourth Amendment search absent additional circumstances. The ALPR caselaw typically focuses instead on the related question of whether law enforcement queries of certain databases containing ALPR information amount to a Fourth Amendment search. No federal appellate court has decided that issue, although one circuit court judge discussed it in a concurrence. A number of federal trial courts and some state courts have upheld law enforcement access to such databases, while cautioning that warrantless surveillance through ALPRs could violate the Fourth Amendment in some circumstances. This In Focus provides an overview of ALPRs, select Fourth Amendment caselaw on their use, and congressional considerations. Background on ALPR Technology ALPR systems work by automatically capturing images or videos of passing vehicles. An algorithm then detects and reads the license plates within the photo/video. ALPR technology can also detect and capture additional, related information, including vehicle type and color, global positioning system (GPS) location data, and date and time. These tools also have the potential to identify individuals in the photos/videos through the use of facial recognition technology (FRT). After they catalog the license plate information, ALPR systems can compare these data points against various databases, including hot lists, which contain a list of license plates linked to vehicles of interest. If there is a match to a hot list license plate, the ALPR system can alert a law enforcement officer in real time. The retention of data from ALPR systems can also help law enforcement track where vehicles have been over time. ALPR use is more common in larger law enforcement agencies than in smaller agencies. According to the Bureau of Justice Statistics, nearly 90% of sheriffs' offices with 500 or more sworn deputies reported using the technology, and 100% of police departments serving over 1 million residents used ALPRs. The Fourth Amendment and ALPRs The Fourth Amendment prohibits unreasonable searches and seizures and provides that no warrants shall issue, but upon probable cause. A search for purposes of the Fourth Amendment generally involves (1) government intrusion upon a person's reasonable expectation of privacy, or (2) government trespass upon a constitutionally protected space. If law enforcement activity is not considered a Fourth Amendment search or seizure, the Fourth Amendment inquiry typically comes to an end. If law enforcement engages in a search or seizure, courts probe whether law enforcement has a warrant, as the Supreme Court has generally established that a search or seizure conducted without a warrant is presumptively unreasonable. If there is no warrant, courts ask whether an exception to the warrant requirement applies, as the Supreme Court has identified certain well-delineated situations in which a warrant is not needed. Third-Party Doctrine and Carpenter The Supreme Court has held that a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties. This concept- known as the third-party doctrine-reflects a judgment that a person takes the risk, in revealing his affairs to another, that the information will be conveyed by that person to the Government. In 2018, the Supreme Court recognized a narrow limitation to the potentially more expansive scope of the third-party doctrine in Carpenter v. United States. That case involved the warrantless search of historical cell-site location information (CSLI)-data recording the location of a cellular device when it connects to a set of radio antennas called 'cell sites,' typically mounted on towers or structures. The Carpenter Court held that the CSLI was not exempt from Fourth Amendment protection pursuant to the third-party doctrine, even though the CSLI was shared by the defendant with cellular providers in the course of his cell phone use. Given the Court's observation that CSLI is generated automatically and its view that carrying a cell phone is indispensable to participation in modern society, it rejected the argument igross.gov