Issue: Automated License Plate Reader (ALPR) Technology

Frequently Asked Questions

What is ALPR technology?

• An ALPR camera automatically captures an image of a passing vehicle’s license plate and transforms that image into alphanumeric characters. The resulting scans can then be compared to a “hotlist” or other database for matching. It is critical to understand that there are many varying use cases for this technology that are completely unrelated to law enforcement investigations and involve entirely different datasets—from ALPR for operational and business purposes like parking, payments, access control and premise security to ALPR for public purposes like traffic enforcement, tolling and school bus enforcement.

What is ALPR data?

• ALPR technologies take a point-in-time image of vehicles at a specific location. For law enforcement and public safety purposes, this is usually on a public roadway recording vehicle plate numbers. A vehicle’s license plate number is required by law to be displayed and observable at any time, so it will always be publicly visible. The distinction between this public nature of license plate numbers and vehicular travel versus personally identifiable information under U.S. laws has been a significant source of confusion concerning the collection and use of ALPR data.
• ALPR data does not identify a specific occupant, as plate numbers and vehicle registration/driver’s license data are not the same. The latter can only be accessed for authorized purposes under the federal Driver's Privacy Protection Act (DPPA), which restricts access and prohibits the release of personal information from state motor vehicle records to ensure the privacy of citizens. These are often conflated, as ALPR systems do not provide access to registration or driver data. The registered owner of a vehicle and other personal information can only be found by searching for separate, secure government databases of license plate records, which are subject to strict controls and audit requirements under the DPPA.

How should constitutional protections be safeguarded when using ALPR systems?

• Fixed and mobile ALPR systems used for public safety purposes record intermittent locations of vehicles on public roads and direction of travel. Law enforcement use of such data is subject to constitutional limitations, and ALPR can be deployed in a way that enhances public safety without violating privacy. U.S. courts have consistently rejected challenges to specific applications of ALPR on Fourth Amendment grounds, clarifying that there not an expectation of privacy on public roads as there would be in private spaces or with respect to private data.
• For example, in United States v. Porter (March 2026), where the court ruled that querying an ALPR system does not constitute a Fourth Amendment “search,” in part because it documents what any bystander could see on a public street. While it speculated as to whether the Fourth Amendment would be implicated (hypothetically) under much more pervasive/long-term tracking using ALPR, this is not how such systems are used today. Earlier in 2026, a federal court ruling in Schmidt v. City of Norfolk (January 2026) concluded essentially that the Virginia city’s deployment of ALPR cameras and collection of ALPR data did not approach the level of tracking that would amount to an unconstitutional search, stating the “limited number of photographs available on a 21-day rolling basis from 75 camera track clusters in Norfolk does not ‘track’ the whole of a person’s movements nor does it provide an ‘intimate’ window into where citizens drive, park, visit, linger, sleep, or patronize.” The case is currently on appeal.
• Most recently—and contrary to mischaracterizations by some critics – the Supreme Court’s decision in Chatrie v. United States (July 2026) clearly distinguished comprehensive third-party location history from point-in-time public-road plate reads. While it held that individuals retain a reasonable expectation of privacy in location data even when held by a third party, it contrasted phone location history with observations “confined to public roads” using “public-movements-only technology.”
• This is fundamentally different than comprehensively tracking the movements of a specific targeted individual over time. For example, the Supreme Court earlier held in United States v. Jones (2012) that physically attaching a GPS tracking device to a vehicle to monitor its movements over weeks is a Fourth Amendment search requiring a warrant, as both physical trespass and continuous tracking are involved. It later held the same in Carpenter v. United States (2018) regarding long-term digital tracking via agency access to cell phone data (which notably includes locations like homes and other private places).

What about "warrantless" use of ALPR systems?

• Considering constitutional questions about ALPR, an understanding of basic U.S. criminal law and investigative procedures when it comes to warrants is critical. Like other lawful sources of information, investigators often use ALPR systems to find a “lead” in historical data that is then used to find other further confirming evidence and establish probable cause (prerequisite for a search or arrest warrant concerning a suspect) – not the other way around. And when it comes to finding missing or endangered persons, there is often no crime involved (or yet known) and thus no relevancy to warrants.
• Much like a security camera creates a record of events in a particular space, after an incident data from an ALPR camera later can be used to help establish that a specific vehicle was in a certain place at a certain time. Importantly, if an ALPR system records a plate number from a passing vehicle, this does not mean that vehicle is being tracked or queried. Investigators would only see this information if it potentially matches a specific query.
• While “hotlists” provide an alert regarding a possible match in ALPR data to lists of stolen vehicles or those connected to other crimes, such alerts do not constitute probable cause. Courts and standard law enforcement procedures treat this as an investigative lead only. Independent verification steps must be taken for such an alert to be elevated to the threshold of reasonable, articulable suspicion that is required to make a traffic stop, or probable cause that is required to conduct a search or arrest.
• The anonymous comparison of plate information using ALPR systems can only work by distinguishing a potential match from nonmatching information. There is no way to predict whether a match would be found prior to a query and no way to even conduct a query unless the comparison data is collected in the first place. Attaching a warrant requirement to ALPR not only makes little sense from a legal standpoint—it would also ultimately make the technology untenable, either as an investigative tool or to address emergency situations.

How should policymakers address concerns about ALPR?

• Concerns about ALPR are focused on law enforcement use of the technology and fall into several categories. These can be addressed though policies applicable to agencies in three areas: 1) privacy safeguards, 2) preventing willful misuse by individual personnel and 3) mitigating the potential for operational or procedural failures (see below). For example, many states with comprehensive ALPR laws limit the data retention period for plate reads collected by law enforcement agencies to a defined period, require certain audit procedures to ensure adherence to policy and place certain conditions on sharing ALPR data with other agencies.