Police Car Tag Scanners: Understanding Automated License Plate Readers and Privacy Concerns

Automated License Plate Readers (ALPRs), often referred to as Police Car Tag Scanners when mounted on patrol vehicles, are advanced, computer-controlled camera systems designed for high-speed license plate capture. These systems are not limited to police cars; they are also commonly affixed to street poles, traffic lights, highway overpasses, and mobile trailers. Operating automatically, ALPRs document every license plate number that comes into their view, along with precise location coordinates, dates, and times. This comprehensive data set, which frequently includes photographs of the vehicle and sometimes even occupants, is then transmitted to a centralized server for storage and analysis.

Vendors promoting ALPR technology highlight its utility for law enforcement in various capacities. They assert that the collected data can be instrumental in retracing a vehicle’s historical locations, thereby establishing its presence, or absence, at crime scenes. Furthermore, ALPR data is touted as a tool for identifying travel patterns and uncovering potential associations between different vehicles. Law enforcement agencies have the option to broaden the reach of their surveillance by sharing this sensitive information with a vast network of other agencies.

However, the aggregation of ALPR data creates a detailed and potentially intrusive record of an individual’s movements, raising significant privacy concerns and potentially chilling First Amendment-protected activities. The technology’s capacity to track vehicles visiting sensitive locations such as healthcare facilities, immigration support centers, gun stores, labor union offices, protest sites, or places of worship is particularly alarming.

Given the mandatory nature of license plates on all registered vehicles, drivers have no choice but to display them publicly. This lack of control underscores the unsettling nature of automated license plate readers, which continuously monitor and record the movements of millions of ordinary citizens, the overwhelming majority of whom have no connection to criminal activity.

How Police Car Tag Scanner Systems Work

Automated license plate reader systems, including police car tag scanners, can be categorized into three main types based on their deployment:

Stationary or Fixed ALPR Cameras

Stationary ALPR cameras mounted on a traffic signal, used for automated license plate recognition and vehicle tracking.

Stationary, or fixed, ALPR cameras are permanently installed in specific locations. Common placements include traffic signals, utility poles, facility entrances, and freeway exit ramps. These cameras are designed to capture license plates of vehicles in motion as they pass within their field of view.

The strategic deployment of multiple stationary ALPR cameras along a roadway enables the tracking of a vehicle’s direction and speed. With a sufficiently dense network of these cameras, law enforcement can achieve real-time vehicle tracking. Moreover, the long-term storage of this data allows authorities to access a historical record of every instance a particular license plate has been detected at a given location. This capability can be used to infer a driver’s likely residence or workplace. Some smaller municipalities have adopted ALPRs at town entrances and exits, effectively creating a surveillance perimeter around their communities. In some instances, ALPR cameras are concealed within objects designed to blend into the environment, such as traffic cones or even artificial cacti.

ALPR technology is frequently integrated with other automated systems, such as red-light and speed enforcement cameras, and is also utilized for electronic toll collection on highways and bridges.

Mobile ALPR Cameras

Mobile ALPR system affixed to a police car, enabling real-time license plate scanning while on patrol.

Mobile ALPR systems, functioning as police car tag scanners, are typically mounted on police patrol vehicles. This mobile deployment allows law enforcement officers to gather license plate data as they patrol city streets throughout their shifts. In many cases, these systems are activated at the start of a shift and remain operational until the shift concludes, continuously capturing data.

Mobile ALPR cameras are not only effective at capturing plates of moving vehicles but also those of parked cars. For instance, a patrol car equipped with a mobile ALPR can systematically scan hundreds of vehicles parked in a public parking lot within minutes, significantly enhancing data collection efficiency.

Police also utilize mobile ALPRs for a practice known as “gridding.” This involves systematically driving an ALPR-equipped vehicle along every street in a neighborhood to collect license plate information on all residents, creating a comprehensive surveillance map.

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

ALPR Trailers

ALPR trailer deployed by police, equipped with license plate reader technology for temporary surveillance in specific areas.

ALPR systems are also available as towable trailers, offering a flexible surveillance solution. Law enforcement can deploy these ALPR trailers to specific locations and leave them to operate for extended periods. ALPR trailers function similarly to fixed ALPR cameras, collecting data without requiring permanent installation. The Drug Enforcement Administration (DEA) has previously acquired these systems, disguised as speed enforcement trailers, to monitor vehicles in areas along the U.S.-Mexico border. Additionally, police have strategically parked trailers or ALPR-equipped vehicles near gun shows and political rallies to monitor attendees.

ALPR Databases

The vast amounts of data collected by ALPR systems, including police car tag scanners, are typically stored in databases for extended periods, often up to five years or more. These databases may be managed by police departments themselves or by private companies such as Vigilant Solutions and Flock Safety. Law enforcement agencies that do not operate their own ALPR systems can still access data collected by other agencies through regional data-sharing networks and platforms managed by these private companies. Notably, several companies operate independent, non-law enforcement ALPR databases, contracting with private vehicle owners to install cameras and collect data. This commercially gathered data is then sold to various entities, including insurance companies, and is also available to law enforcement agencies through subscription services.

Hotlists

Law enforcement agencies frequently utilize “hotlists,” which are pre-loaded lists of license plates that the ALPR system actively searches for. These lists typically include plates associated with stolen vehicles or vehicles linked to outstanding warrants. Police officers can also create their own hotlists for specific investigations. When an ALPR camera scans a plate that matches an entry on a hotlist, the system immediately sends an alert to the officer in the patrol car (for mobile ALPRs) or to the relevant agency (for fixed ALPRs). Some hotlists include plates linked to low-level misdemeanors and even traffic violations, raising concerns about the scope of surveillance. In some instances, agencies use these hotlists to generate revenue by targeting individuals with unpaid citations.

What Kinds of Data a Police Car Tag Scanner Collects

Police car tag scanners and other ALPR systems collect a range of data, including license plate numbers, location data, and precise date and time stamps for each plate encounter. Some advanced systems are also capable of capturing the make and model of the vehicle. These systems are incredibly efficient, with the capacity to scan thousands of license plates per minute. One vendor boasts a dataset exceeding 6.5 billion scans, growing by an astonishing 120 million data points each month, illustrating the massive scale of data collection.

By combining data from multiple ALPR encounters, law enforcement can determine a vehicle’s direction and speed through triangulation. Aggregated over time, this data reveals a detailed history of a vehicle’s movements. Sophisticated algorithms can be applied to this data to identify regular travel patterns and even predict a driver’s future locations. Furthermore, ALPR data can reveal all vehicles that have visited a specific location over a given period.

While ALPR data typically does not include the driver’s name directly, law enforcement agencies possess the capability to cross-reference license plate numbers with other databases to link plates to individual identities.

Beyond license plate data, the photographs captured by ALPR systems can reveal images of the vehicle itself, its occupants (drivers and passengers), and the immediate surroundings. In some cases, these images can even capture people entering or exiting vehicles. Certain ALPR products create “vehicle fingerprints,” which include additional details such as vehicle color, make, model, physical damage, and bumper stickers, further enhancing vehicle identification capabilities.

How Law Enforcement Uses Police Car Tag Scanner Technology

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Time-lapse visualization of license plate data collected by police car tag scanners in Oakland, demonstrating the extensive reach of ALPR surveillance.

Police car tag scanners and ALPR technology gather data indiscriminately, collecting information on a vast number of ordinary citizens. By mapping vehicle times and locations and tracking past movements, law enforcement can utilize stored data to create detailed profiles of drivers’ lives, identify behavioral patterns, and potentially even predict future actions. This level of surveillance is achieved despite the fact that the vast majority of individuals whose license plate data is collected are not suspected of any crime. Prior to ALPR technology, law enforcement relied on manual license plate recording, which was time-consuming and limited the volume of data collection. ALPR technology removes these limitations, enabling the rapid and broad collection of license plate data with significantly reduced manpower requirements.

A 2021 report by the EFF analyzing data from 63 California law enforcement agencies revealed that only 0.05% of the data collected by ALPRs was relevant to a public safety interest at the time of capture, highlighting the disproportionate collection of data on non-suspect individuals.

Law enforcement agencies primarily employ police car tag scanners and ALPR technology for two main purposes:

Real-time Investigations

By adding a license plate to a “hotlist,” officers can leverage ALPR systems to automatically identify and track specific vehicles in real time. License plates are commonly added to hotlists if a vehicle is reported stolen or associated with an outstanding warrant. Officers may also add plates if a vehicle has been observed at a crime scene, if the owner is a suspect in an investigation, or if the vehicle is believed to be linked to gang activity. However, hotlists often extend to low-level offenses as well, expanding the scope of real-time monitoring.

Historical Investigations

Since ALPR systems, including police car tag scanners, collect data on virtually all vehicles, law enforcement can search and analyze historical data using a license plate, partial plate information, or a physical address. For example, an officer investigating a convenience store robbery could input the store’s location into an ALPR database to identify vehicles that were present nearby at the time of the incident. The officer can then trace those plate numbers to uncover other locations where the same plates have been recorded, potentially establishing patterns or connections.

It is important to note that training materials, policies, and legal guidelines in some jurisdictions caution officers that a hotlist alert alone may not be sufficient justification for a vehicle stop. Officers are typically instructed to visually confirm the plate match. Failures in manual confirmation, combined with occasional machine errors, have resulted in wrongful stops, underscoring the need for careful verification.

While law enforcement agencies often cite successful cases involving ALPR data, such as recovering stolen vehicles or locating abducted children, police have also utilized this technology for mass enforcement of less serious offenses. Examples include identifying uninsured vehicles or tracking down individuals with overdue court fees, raising concerns about the appropriate application of ALPR technology.

The retention period for ALPR data varies significantly across agencies, ranging from just a few days to several years. However, some entities, particularly private companies, may retain data indefinitely, further amplifying privacy concerns.

Who Sells Police Car Tag Scanner Technology

Several companies specialize in the development and sale of ALPR technology, including police car tag scanners. Vigilant Solutions (a subsidiary of Motorola Solutions) and Flock Safety are among the most prevalent ALPR vendors in the United States. Other notable vendors in the market include Rekor, Elsag, Axon, Perceptics, and Jenoptik.

Vigilant Solutions, through its affiliated company Digital Recognition Network, provides access to a vast database of license plate data collected privately through partnerships with vehicle repossession companies. These companies passively collect ALPR data using their own vehicles, contributing to the expansive commercial database. Flock Safety has established similar partnerships with numerous homeowners associations, enabling data sharing with law enforcement. Both Vigilant Solutions and Flock Safety facilitate data sharing among law enforcement agencies nationwide, creating extensive interconnected surveillance networks.

Threats Posed by Police Car Tag Scanners

Police car tag scanners and ALPR technology, while presented as tools for law enforcement, pose significant threats to individual privacy and can potentially infringe upon the rights of entire communities.

Instances of abuse of this technology by law enforcement agencies have been documented. In one case, New York City police officers systematically recorded the license plate numbers of all vehicles parked near a mosque. In Birmingham, UK, police targeted a Muslim community with surveillance while misrepresenting the project’s nature to the public. EFF analysis of Oakland Police Department ALPR data revealed a pattern of disproportionate deployment of ALPR-equipped vehicles in low-income neighborhoods and communities of color, raising concerns about discriminatory surveillance practices.

Furthermore, individual officers have been found to misuse law enforcement databases, including license plate information and motor vehicle records, for personal gain. For example, a Washington, D.C. police officer was convicted of extortion after using license plate lookups to identify patrons of a gay bar and subsequently blackmailing them. More recently, a police lieutenant in Kechi, Kansas, was arrested for allegedly accessing a Flock Safety ALPR database to stalk his estranged wife, demonstrating the potential for abuse even with systems designed for law enforcement use.

In addition to intentional misuse, ALPR systems are susceptible to errors in plate reading, which can lead to severe consequences. In a disturbing incident in San Francisco, a woman was forcibly pulled from her car at gunpoint due to a license plate reader error that misidentified her vehicle as stolen. This incident led the U.S. Ninth Circuit Court of Appeals to rule that technology alone cannot justify such a stop, although this ruling does not apply nationwide, leaving individuals vulnerable to similar errors. More recently, in Aurora, Colorado, a group of Black youths were traumatized by police after an ALPR system incorrectly flagged their vehicle as stolen, highlighting the potential for racial bias and harm.

The long-term storage of aggregated ALPR data significantly increases its invasiveness and vulnerability to misuse and data breaches. Even U.S. Customs and Border Protection, a well-resourced federal agency, experienced a data breach when its ALPR vendor, Perceptics, was hacked, and sensitive data was leaked online. Implementing sensible data retention limits, clear policies on data access within agencies, and robust audit and control processes are crucial steps to mitigate these risks. Ideally, a strong privacy protection measure would involve police retaining no data at all when a scanned vehicle does not match a hotlist, minimizing the collection of data on innocent individuals.

Police car tag scanners and ALPR systems can also be misused to target specific communities, such as immigrant populations and individuals seeking or providing reproductive healthcare services, raising concerns about the technology’s potential to chill constitutionally protected activities.

EFF’s Work on ALPR

The Electronic Frontier Foundation (EFF) has been actively engaged in investigating and addressing the privacy threats associated with ALPR technology since 2012 through public records requests, litigation, and legislative advocacy.

ALPR Litigation

EFF, in collaboration with the ACLU of Southern California, filed lawsuits against the Los Angeles County Sheriff’s Department and the Los Angeles Police Department after these agencies refused to disclose ALPR data, claiming it was exempt from the California Public Records Act as investigative records. This argument was challenged as implying that all residents of Los Angeles were under investigation, a notion deemed “Orwellian” during court proceedings. In 2017, the California Supreme Court ruled in favor of EFF and ACLU, ordering the case back to the lower court and establishing a precedent for public access to ALPR data.

In 2021, EFF and the ACLU also represented local activists in Lagleva v. Marin County Sheriff, suing the Marin County Sheriff’s Office for unlawfully sharing ALPR data with out-of-state agencies, including Immigration & Customs Enforcement (ICE), in violation of California law. A settlement was reached in which the sheriff agreed to cease data sharing outside of California, reinforcing protections against the misuse of ALPR data for immigration enforcement.

Beyond California, EFF has filed amicus briefs in legal challenges to excessive ALPR data collection and storage in Virginia, Massachusetts, and Nevada, advocating for stronger privacy protections in the context of vehicle surveillance.

ALPR Accountability and Transparency

In 2015, the California legislature enacted S.B. 34, a bill designed to enhance ALPR data protection, requiring user agencies to implement data protection measures, maintain access logs, hold public meetings prior to ALPR program implementation, establish usage and privacy policies, and maintain access logs. The law also restricts the sale, sharing, or transfer of ALPR data to public agencies only.

EFF has coordinated volunteer efforts to collect ALPR policies from agencies across California and to expose agencies failing to comply with S.B. 34. Through its Data Driven and Data Driven 2 projects, EFF has independently filed public records requests with numerous agencies to shed light on their ALPR data usage practices, promoting transparency and accountability.

In 2019, EFF successfully advocated for a California State Legislature audit of law enforcement agencies’ compliance with S.B. 34. The California State Auditor subsequently issued a critical report confirming EFF’s concerns about agency non-compliance, inadequate policies, and overly broad data sharing practices.