Car Tag Scanners: Understanding Automated License Plate Readers and Their Impact

Automated License Plate Readers (ALPRs), also known as Car Tag Scanners, are sophisticated, computer-vision camera systems designed for rapid license plate capture. These systems are commonly deployed in various locations, from street poles and traffic lights to highway overpasses and police vehicles. Operating at high speed, car tag scanners automatically record license plate numbers that fall within their field of view, along with crucial contextual data including location, date, and time stamps. This rich data, often accompanied by photographs of the vehicle and sometimes even occupants, is then transmitted to a centralized server for storage and analysis.

According to vendors like Vigilant Solutions, the data collected by car tag scanners offers law enforcement agencies a powerful toolset. By analyzing historical location data, police can determine a vehicle’s whereabouts over time, ascertain its presence at crime scenes, identify travel patterns, and even uncover associations between different vehicles. Furthermore, law enforcement agencies have the option to share this extensive database with a vast network of other agencies, amplifying the reach and scope of vehicle tracking capabilities.

However, the aggregated nature of car tag scanner data raises significant privacy concerns. The detailed records can paint an incredibly intimate picture of an individual’s life, potentially chilling activities protected by the First Amendment. This technology could be used to monitor drivers visiting sensitive locations such as healthcare facilities, immigration support centers, gun stores, labor union offices, protest sites, or places of worship.

Given the mandatory display of license plates on all vehicles operating on public roads, drivers have no agency over whether their vehicles are subject to car tag scanning. This compulsory visibility makes the widespread use of automated license plate readers to track the movements of millions of ordinary citizens particularly concerning, especially considering that the vast majority of these individuals have no connection to criminal activity.

How Car Tag Scanner Systems Operate

Car tag scanners can be broadly categorized into three primary types based on their deployment and functionality.

Stationary or Fixed Car Tag Scanners

Stationary car tag scanners, as the name suggests, are permanently installed in fixed locations. These locations can range from traffic signals and utility poles to building entrances and freeway off-ramps. Typically, these cameras are configured to capture license plates only from vehicles in motion that pass within their designated field of view.

When multiple stationary car tag scanners are strategically positioned along a single roadway, the collected data can reveal not only the direction of travel but also the speed of a vehicle. With a dense enough network of cameras, law enforcement can achieve real-time vehicle tracking. Moreover, the long-term storage of this data allows authorities to access historical records of when a specific license plate passed a particular location. This capability enables inferences about a driver’s likely residence or workplace. In some instances, smaller municipalities have implemented car tag scanners at town entrances and exits, effectively creating a digital perimeter where every vehicle entering or leaving is documented. In efforts to blend these surveillance tools into the environment, police may even disguise car tag scanners as ordinary objects like traffic cones or even cacti.

Stationary car tag scanners are frequently integrated with other automated traffic enforcement systems, such as red-light and speed enforcement cameras. They also serve as a mechanism for automated toll collection on highways and bridges.

Mobile Car Tag Scanners

Mobile car tag scanners are designed for dynamic data collection and are typically mounted on law enforcement patrol vehicles. This mobile deployment allows officers to capture license plate data as they patrol city streets throughout their shifts. In most operational protocols, these systems are activated at the beginning of a shift and remain continuously running until the shift concludes.

Beyond capturing images of moving vehicles, mobile car tag scanners are highly effective at recording license plates of parked vehicles. For example, a patrol car equipped with a mobile scanner can systematically drive through a public parking lot, capturing hundreds of vehicle license plates in a matter of minutes.

Law enforcement agencies also utilize mobile car tag scanners for a practice known as “gridding.” This involves systematically driving an ALPR-equipped vehicle along every street in a neighborhood to gather comprehensive intelligence on residents and vehicle presence within the area.

Furthermore, private companies like Vigilant Solutions operate mobile car tag scanner fleets to collect license plate data independently. This privately collected data is then sold to law enforcement agencies and other interested parties, creating a commercial market for vehicle location information.

Car Tag Scanner Trailers

Car tag scanners are also available in trailer-mounted configurations, providing a flexible and temporary deployment option for law enforcement. These trailers can be towed to specific locations and left in place for extended periods to collect data, functioning similarly to fixed car tag scanners but without requiring permanent installation. The Drug Enforcement Administration (DEA) has historically utilized these trailer systems, sometimes disguised as speed enforcement trailers, to monitor vehicle movements in areas along the U.S.-Mexico border. Police have also strategically deployed trailers or vehicles equipped with car tag scanners near gun shows and political rallies to monitor attendees.

Car Tag Scanner Databases

The vast majority of data gathered by car tag scanners is stored in databases for extended periods, often for as long as five years. These databases may be maintained directly by police departments or, increasingly, by private companies specializing in data management and analysis, such as Vigilant Solutions or Flock Safety. Law enforcement agencies that do not operate their own car tag scanner systems can gain access to data collected by other agencies through regional data-sharing networks and platforms managed by these private companies. In addition to law enforcement-focused databases, several companies operate independent, non-law enforcement car tag scanner databases. These companies contract with individuals to install cameras on private vehicles to collect data, which is then sold to various commercial entities, such as insurance companies. Law enforcement agencies can also purchase subscription-based access to this commercially collected data, further expanding their surveillance capabilities.

Hotlists

Law enforcement agencies commonly utilize “hotlists” in conjunction with car tag scanner systems. These hotlists are pre-loaded lists of license plates that the system is actively programmed to look for, typically including plates associated with stolen vehicles or vehicles linked to outstanding warrants. Police officers also have the capability to create their own hotlists for specific investigations or monitoring purposes. When a car tag scanner detects a license plate that matches an entry on a hotlist, the system immediately sends an alert to the officer in the patrol car (for mobile scanners) or to the relevant agency (for fixed scanners). It’s important to note that some hotlists may include vehicles associated with low-level misdemeanors and even traffic offenses. In some jurisdictions, agencies utilize these hotlists to generate revenue by targeting and stopping vehicles with unpaid citations.

Types of Data Collected by Car Tag Scanners

Car tag scanners collect a range of data points beyond just license plate numbers. Crucially, they record location data along with the precise date and time each license plate is encountered. Advanced systems can also capture the make and model of the vehicle. The speed at which these systems operate is remarkable, with some capable of scanning thousands of license plates per minute. One vendor boasts a dataset exceeding 6.5 billion scans, growing by an astonishing rate of 120 million data points each month.

When car tag scanner data is combined, it can reveal detailed travel information. Triangulation techniques can determine the direction and speed a vehicle traveled. Aggregated data over time paints a comprehensive picture of a vehicle’s historical travel patterns. By applying sophisticated algorithms to this data, systems can identify regular travel routes and even predict a driver’s future locations. The data also inherently reveals all vehicles that have visited a specific location within the scanner’s operational timeframe.

While car tag scanner data typically does not directly include the driver’s name, law enforcement officers possess the ability to cross-reference license plate numbers with other databases, such as Department of Motor Vehicles records, to link individual names to their vehicle registrations.

In addition to license plate data, the photographs captured by car tag scanners can reveal visual information about the vehicle itself, including its type and condition. More significantly, images can capture glimpses of the vehicle’s occupants, including drivers and passengers, as well as the immediate surroundings. In some instances, the imagery may even capture people entering or exiting the vehicle. Certain advanced products create “vehicle fingerprints,” which incorporate additional details such as vehicle color, make, model, physical damage, and even the presence of bumper stickers, creating a highly detailed profile of each vehicle scanned.

How Law Enforcement Utilizes Car Tag Scanner Technology

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A time-lapse visualization of the data collected by Oakland Police Department vehicles mounted with license plate readers.

Car tag scanner data collection is indiscriminate, gathering information on millions of ordinary individuals, the vast majority of whom are not suspected of any wrongdoing. By mapping vehicle times and locations and tracing past movements, police can leverage stored data to construct detailed profiles of drivers’ lives, identifying past behavior patterns and potentially even predicting future actions. This capability exists despite the fact that most individuals whose license plate data is collected and stored have not been accused of any crime. Prior to car tag scanner technology, law enforcement officers had to manually record license plates, a process that imposed practical limitations on data collection and required officers to selectively choose which vehicles to track. Car tag scanners eliminate these limitations, enabling the surveillance of everyone and facilitating faster, broader data collection with significantly reduced staffing requirements.

A 2021 report by the Electronic Frontier Foundation (EFF) analyzing data from 63 California law enforcement agencies revealed that a mere 0.05% of the data collected by car tag scanners was relevant to a public safety interest at the time of capture.

Law enforcement agencies primarily employ car tag scanners for two general purposes: real-time investigations and historical investigations.

Real-Time Investigations

By adding a license plate to a “hotlist,” law enforcement can utilize car tag scanners to automatically identify and track specific vehicles in real time. License plates are commonly added to hotlists when a vehicle is reported stolen or is associated with an outstanding warrant. Officers may also add a plate number if a vehicle has been observed at a crime scene, if the owner is a suspect in a crime, or if the vehicle is believed to be connected to gang activity. It is important to note that hotlists can also include vehicles associated with even low-level offenses.

Historical Investigations

Given that car tag scanners typically collect data on all vehicles, not just those on hotlists, officers can search and analyze historical data using a full or partial license plate number or even a physical address. For example, in the investigation of a convenience store robbery, an officer could input the store’s location to identify all vehicles recorded in the vicinity at the time of the incident. The officer can then further investigate those plate numbers to discover other locations where the same plates have been recorded, potentially establishing patterns or connections.

It is crucial to note that training materials, policies, and laws in some jurisdictions advise officers that a hotlist alert alone may not be sufficient grounds for a vehicle stop. Officers are typically instructed to visually confirm the license plate match before initiating a stop. Failures to manually verify plate numbers, combined with occasional machine errors in plate reading, have resulted in wrongful stops and detentions.

While law enforcement agencies often cite successes in using car tag scanner data to recover stolen vehicles or locate abducted children, the technology has also been applied to mass enforcement of less serious offenses, such as identifying uninsured vehicles or tracking down individuals with overdue court fees.

The data retention period for car tag scanner data varies significantly depending on the agency, ranging from just a few days to several years. However, some entities, particularly private companies that collect and aggregate this data, may retain the information indefinitely.

Vendors of Car Tag Scanner Technology

Vigilant Solutions (a subsidiary of Motorola Solutions) and Flock Safety are prominent vendors in the car tag scanner technology market within the United States. Other companies in this sector include Rekor, Elsag, Axon, Perceptics, and Jenoptik.

Vigilant Solutions, through its affiliated company Digital Recognition Network, offers access to a vast dataset of license plate information that it has privately collected through partnerships with vehicle repossession companies. These repossession companies passively collect car tag scanner data using their own vehicle fleets. Flock Safety similarly has established partnerships with numerous homeowners associations, gaining access to data collected by community-operated car tag scanner systems. Both Vigilant Solutions and Flock Safety offer law enforcement agencies the capability to share data with each other across the country, creating expansive networks of surveillance information.

Privacy and Civil Liberty Threats Posed by Car Tag Scanners

Car tag scanner technology, while presented as a law enforcement tool, presents significant threats to individual privacy and the civil liberties of entire communities if not properly regulated and overseen.

Instances of abuse and misuse of this technology by law enforcement agencies have been documented. In one case, New York City Police Department officers were found to have systematically driven down streets and electronically recorded the license plate numbers of all vehicles parked near a mosque. In Birmingham, UK, police controversially targeted a Muslim community with surveillance, misleading the public about the nature and scope of the project. Data obtained by the EFF from the Oakland Police Department revealed that ALPR-mounted vehicles were disproportionately deployed in low-income communities and communities of color, raising concerns about biased application of surveillance.

Furthermore, individual law enforcement officers have been found to abuse law enforcement databases, including license plate information and records held by motor vehicle departments. In a 1998 case, a Washington, D.C. police officer pleaded guilty to extortion after using license plate lookups to identify vehicle owners parked near a gay bar and then blackmailing them. More recently, a police lieutenant in Kechi, Kansas, was arrested on suspicion of accessing a Flock Safety car tag scanner database to stalk his estranged wife, highlighting the potential for personal misuse of these systems.

Beyond deliberate misuse, car tag scanners are also susceptible to errors in plate reading, which can lead to serious and unwarranted consequences. In a disturbing incident in 2009, San Francisco police pulled over Denise Green, an African-American city worker, handcuffed her at gunpoint, forced her to her knees, and searched both her and her vehicle. This aggressive stop was triggered solely by a car tag scanner error that misidentified her vehicle as stolen. Her experience led to a U.S. Ninth Circuit Court of Appeals ruling that technology alone cannot be the basis for such a stop. However, this ruling is not universally applicable, leaving individuals in other jurisdictions vulnerable to similar law enforcement errors. More recently, in Aurora, Colorado, a group of Black youths were traumatized by police after a car tag scanner system incorrectly flagged their vehicle as stolen, demonstrating the ongoing risk of misidentification and its disproportionate impact on minority communities.

The aggregation of car tag scanner data over extended periods, or indefinite retention, amplifies its invasiveness and potential for abuse. Such vast datasets become attractive targets for both misuse and data breaches. Even U.S. Customs & Border Protection, a well-resourced federal agency, experienced a security breach when its car tag scanner vendor, Perceptics, was hacked and sensitive data published online. Implementing sensible data retention limits, clear policies regarding data access within agencies, and robust audit and control processes are crucial steps to mitigate these risks. Ideally, from a privacy perspective, police agencies would retain no data at all when a scanned vehicle does not match a hotlist, minimizing the collection and storage of data on law-abiding citizens.

Car tag scanners also pose a particular threat to vulnerable communities, as they can be used to target immigrant communities and individuals seeking or providing reproductive healthcare services, raising concerns about the technology’s potential to chill access to essential services and infringe on fundamental rights.

EFF’s Advocacy and Legal Work on Car Tag Scanners

The Electronic Frontier Foundation (EFF) has been actively engaged in investigating and challenging the privacy threats posed by car tag scanner technology since 2012 through public records requests, litigation, and legislative advocacy.

Car Tag Scanner Litigation

In a significant legal challenge, EFF and the ACLU of Southern California jointly sued the Los Angeles County Sheriff’s Department and the Los Angeles Police Department after these agencies refused to disclose car tag scanner data in response to public records requests. The agencies argued that the data was exempt from the California Public Records Act, claiming it constituted investigative records. This argument effectively asserted that all residents of Los Angeles were under investigation, a premise that was described as “Orwellian” by both an LAPD lawyer and a California Supreme Court Justice during oral arguments. In a landmark 2017 ruling, the California Supreme Court sided with EFF and the ACLU, ordering the case back to the Superior Court and establishing a precedent for public access to this type of data.

EFF and the ACLU also pursued legal action against the Marin County Sheriff’s Office in 2021 on behalf of local activists in Lagleva v. Marin County Sheriff. This lawsuit challenged the sheriff’s practice of sharing car tag scanner data with out-of-state agencies, including Immigration & Customs Enforcement (ICE), in violation of California laws regulating ALPR use and prohibiting the sharing of criminal justice data for immigration enforcement. As part of a settlement agreement, the sheriff agreed to cease sharing data outside of California, setting an important limitation on interstate data sharing.

Beyond California, EFF has filed amicus briefs in legal cases concerning car tag scanner data collection and use in other states, including Virginia, Massachusetts, and Nevada, advocating for stronger privacy protections for drivers and limitations on law enforcement surveillance.

Car Tag Scanner Accountability and Transparency Efforts

In 2015, the California legislature passed S.B. 34, a bill championed by privacy advocates, which mandates that car tag scanner users implement data protection measures, maintain access logs, hold public meetings before initiating ALPR programs, establish usage and privacy policies, and maintain detailed access logs. The law also prohibits public agencies from selling, sharing, or transferring car tag scanner data, except to other public agencies, aiming to limit the commercialization and broad dissemination of this sensitive information.

EFF has coordinated volunteer efforts to collect and analyze car tag scanner policies across California, working to expose agencies that are failing to comply with S.B. 34 and other transparency requirements. Through projects like Data Driven and Data Driven 2, EFF has independently filed public records requests with numerous agencies to shed light on their car tag scanner data collection practices and usage patterns, contributing to greater public awareness and accountability.

In 2019, EFF successfully advocated for the California Legislature to order a state audit of several law enforcement agencies’ compliance with S.B. 34. The resulting California State Auditor report substantiated many of EFF’s concerns, revealing that agencies were indeed not fully adhering to the law, lacked adequate policies, and were sharing data too broadly, reinforcing the need for stronger oversight and regulation of car tag scanner technology.