The surveillance camera on your street corner: lawful spying or constitutionally problematic?

The cameras that scan your car on your commute to work have quietly become one of the most widespread surveillance tools in America. 

They record vehicle sightings, feed searchable databases and, when agencies choose to share data, can connect searches across jurisdictional lines. 

Recent courts have upheld the particular ALPR networks before them, but they have left open whether a denser, more revealing system could cross the constitutional line.

What are ALPRs? 

Automated license plate readers (ALPRs), which are usually small, solar-powered cameras mounted on a pole, building or police car, capture and record where tens of millions of drivers go every day. Flock Safety, one of the leading ALPR vendors, has exploded in popularity with law enforcement, municipalities and businesses in recent years.

Flock's own marketing claims that it is present in more than 6,000 communities, working with more than 1,000 businesses, and more than 5,000 law enforcement agencies nationwide, resulting in billions of vehicle scans per month.

How it works:

ALPRs photograph every passing car, capturing details like license plate number, make, model, color, and other distinguishing features like roof racks, bumper stickers, and scratches to create what Flock calls a "vehicle fingerprint." 

This information is then uploaded to a searchable database that can be shared with other agencies when the owning department enables it, typically without a warrant.

Privacy concerns abound. 

Privacy advocates, online creators, and concerned citizens argue that the concern isn't any single photograph but the aggregate data. A dense, searchable, cross-jurisdictional archive, they contend, can reconstruct a person's movements, associations and routines over time, providing a mosaic of a person's life all without a warrant.

In a review of Flock audit logs, the Electronic Frontier Foundation reported finding searches associated with protest activity. 

Advocates also point to reported misuse, including allegations that officers ran searches to track partners or acquaintances, and cases in which drivers were stopped and even held at gunpoint after an inaccurate plate scan.

But law enforcement say the tools help them solve crimes more efficiently. 

Police departments and Flock counter that a license plate is displayed in public, that officers see only what any bystander can, and that the tool helps them solve crimes more efficiently. 

Flock points to data retention limits, user accounts, and audit logs, and cites company data claiming its technology supports more than a million investigations a year.

What does the law say? 

Courts have long held that, generally, there is no reasonable expectation of privacy of movements when traveling in an automobile on public roads and with license plate information that is exposed to public view.

In Schmidt v. City of Norfolk, a pending appeal before the Fourth Circuit Court of Appeals, two plaintiffs, one a Norfolk resident and the other a frequent commuter through the city, argued that the city's 176 cameras - retaining 21 days of images - let police retrace residents' movements without a warrant. 

Notably, building on the 2018 Carpenter decision, the Supreme Court ruled last month in Chatrie v. United States that police conduct a Fourth Amendment search when they obtain a person's Google Location History (the record of location data that Google keeps on its users). 

Though Chatrie involved cell-phone data, not license plate records, ALPR critics claim that Chatrie strengthens the argument that a searchable archive of someone's past movements is constitutionally different from a single observation. 

However, while cellphones can follow someone continuously, ALPR systems are generally fixed to a static location.

Meanwhile, Rep. Tim Burchett (R-Tenn.) proposed the "Protection Against Mass Surveillance Act" this week to prohibit the federal government from purchasing or using mass tracking tools, in addition to banning states from using federal funding for the same systems. 

Saying we need to "ban these dadgum" things, Burchett argues the cameras are warrantless surveillance tools that violate the Fourth Amendment, saying that Americans should never choose between safety and liberty.

Pryce Renfroe contributed to this report.