Require Police to Get a Warrant to Search ALPR Data

This post was co-written by Andi Cao, an EFF legal intern.

Automated license plate readers (ALPRs) are mass surveillance. They photograph every passing car and log where and when it was captured, building a searchable record of where nearly everyone drives. Cities should not buy them, and cities that already have them should shut them down.

Where these systems still operate, courts and state legislatures must reduce their harms by (among other things) requiring police to get a warrant before searching stored ALPR data. A warrant requirement would not make mass surveillance acceptable, but it would require police to justify a search to a judge before accessing records of people’s movements. Without this independent judicial check on police power, officers have been searching this data for improper reasons (many exposed by EFF) that violate our fundamental rights.

A warrant requires a judge to find probable cause and specificity—many warrantless police searches of ALPR data lack both. Officers have searched this data to profile Romani people, monitor protesters, investigate an abortion, find immigrants for deportation, track a man who complained about a deputy, stalk romantic partners, and even for no stated reason beyond “LMAO.” A warrant requirement would force law enforcement to justify these searches before accessing sensitive location records, not leave the people they target to discover and challenge the abuse after the harm is done.

What a Warrant Requires

Warrants are a check on police power. Before officers can search a person or their property, the Fourth Amendment requires them to convince a neutral judge, under oath, that probable cause exists, meaning a fair probability the search will turn up evidence of a crime. The warrant must also describe with particularity what will be searched, so police cannot go on a fishing expedition. Critically, the officer who wants to search is not the person who decides whether the search is justified.

That is why warrants are required for so many kinds of police surveillance. For example, police generally need a warrant to wiretap phone calls, to search the contents of a cell phone, and to obtain historical cell phone location records.

Stored ALPR data reveals sensitive information about the private details of our lives: where we go, when, and with whom. That’s why we believe police searches of stored ALPR data should also require a warrant. Earlier this month, a federal judge in Oklahoma agreed.

What Goes Wrong Without a Warrant: San Jose, California

San Jose demonstrates the harmful consequences of letting law enforcement search stored ALPR data without a warrant. EFF and the ACLU of Northern California represent SIREN and CAIR-California in a lawsuit challenging this practice.

The first problem is the sheer number of times that SJPD officers search stored ALPR data: 261,711 times between June 5, 2024, and June 17, 2025, about 692 searches a day. That scale is the result of having no warrant requirement, which would greatly reduce this kind of casual police surveillance.

Inevitably, officers abuse this unchecked power. In September, San Jose’s police chief disclosed an example from five months earlier: the department had fired an officer who used its ALPR system to track a woman who had accused his cousin of domestic violence, and then shared her location information with his cousin. The abusive search of stored ALPR data came to light only after the woman told police that her alleged assailant had implied he was tracking her.  A warrant requirement would have prevented this.

Of course, similar problems appear nationwide. For each examp