This post was co-authored by EFF legal intern Olivia Miller. For most Americans—driving is a part of everyday life. Practically speaking, many of us drive to work, school, play, and anywhere in between. Not only do we visit places that give insights into our personal lives, but we sometimes use vehicles as a mode of displaying information about our political beliefs, socioeconomic status, and other intimate details. All of this personal activity can be tracked and identified through Automatic License Plate Reader (ALPR) data—a popular surveillance tool used by law enforcement agencies across the country. That’s why, in an amicus brief filed with the Virginia Court of Appeals, EFF, the ACLU of Virginia, and NACDL urged the court to require police to seek a warrant before searching ALPR data. In Commonwealth v. Church, a police officer in Norfolk, Virginia searched license plate data without a warrant—not to prove that defendant Ronnie Church was at the scene of the crime, but merely to try to show he had a “guilty mind.” The lower court, in a one-page ruling relying on Commonwealth v. Bell, held this warrantless search violated the Fourth Amendment and suppressed the ALPR evidence. We argued the appellate court should uphold this decision. Like the cellphone location data the Supreme Court protected in Carpenter v. United States, ALPR data threatens peoples’ privacy because it is collected indiscriminately over time and can provide police with a detailed picture of a person’s movements. ALPR data includes photos of license plates, vehicle make and model, any distinctive features of the vehicle, and precise time and location information. Once an ALPR logs a car’s data, the information is uploaded to the cloud and made accessible to law enforcement agencies at the local, state, and federal level—creating a near real-time tracking tool that can follow individuals across vast distances. Think police only use ALPRs to track suspected criminals? Think again. ALPRs are ubiquitous; every car traveling into the camera’s view generates a detailed dataset, regardless of any suspected criminal activity. In fact, a survey of 173 law enforcement agencies employing ALPRs nationwide revealed that 99.5% of scans belonged to people who had no association to crime. Norfolk County, Virginia, is home to over 170 ALPR cameras operated by Flock, a surveillance company that maintains over 83,000 ALPRs nationwide. The resulting surveillance network is so large that Norfolk county’s police chief suggested “it would be difficult to drive any distance and not be recorded by one.” Recent and near-horizon advancements in Flock’s products will continue to threaten our privacy and further the surveillance state. For example, Flock’s ALPR data has been used for immigration raids, to track individuals seeking abortion-related care, to conduct fishing expeditions, and to identify relationships between people who may be traveling together but in different cars. With the help of artificial intelligence, ALPR databases could be aggregated with other information from data breaches and data brokers, to create “people lookup tools.” Even public safety advocates and law enforcement, like the International Association of Chiefs of Police, have warned that ALPR tech creates a risk “that individuals will become more cautious in their exercise of their protected rights of expression, protest, association, political participation because they consider themselves under constant surveillance.”   This is why a warrant requirement for ALPR data is so important. As the Virginia trial court previously found in Bell, prolonged tracking of public movements with surveillance invades peoples’ reasonable expectation of privacy in the entirety of their movements. Recent Fourth Amendment jurisprudence, including Carpenter and Leaders of a Beautiful Struggle from the federal Fourth Circuit Court of Appeals favors a warrant requirement as well. Like the technologies at issue in those cases, ALPRs give police the ability to chronicle movements in a “detailed, encyclopedic” record, akin to “attaching an ankle monitor to every person in the city.”   The Virginia Court of Appeals has a chance to draw a clear line on warrantless ALPR surveillance, and to tell Norfolk PD what the Fourth Amendment already says: come back with a warrant.