What are license plate readers?

The short version

An automated license plate reader (ALPR) is a camera that photographs passing vehicles and reads their plates by software. Each read is saved with the time and place it was taken. Put enough of them along a city’s roads and the records show where a vehicle has been, and when.

How they work

• The camera. Most are fixed on poles, traffic signals or overpasses. Some ride on police cars, tow trucks or trailers.
• The read. Software turns the plate in each photo into text. Many systems also note the vehicle’s make, color or other visible features, and keep the photo itself.
• The check. Reads are usually compared against “hot lists”, such as stolen vehicles, Amber Alerts or wanted plates, and can trigger an alert within seconds.
• The record. Reads are stored for a period set by the operator, the vendor contract or state law. That can be days or years. Some networks let other agencies search them.

Who runs them

Police departments and sheriff’s offices run most public-road cameras. Others are run by toll and transportation agencies, cities, homeowner associations, shopping centers, parking operators and vehicle repossession companies. Many are leased from vendors who host the data, and Flock Safety is one of the largest.

Why people disagree about them

Supporters point to stolen cars recovered, missing people found and crimes solved faster. Critics point to records kept on millions of drivers who aren’t suspected of anything, data shared beyond the agency that collected it, and misread plates that have led to wrongful stops. Both are part of the public debate, and the rules differ a lot from place to place.

NitoPath doesn’t take a side. Some people use it to pass fewer cameras, others to stay on monitored roads. Either way, it starts with knowing where they are.

How to find the rules where you live

1. Search your city or county’s website for “license plate reader” or the vendor’s name. Council agendas often include the contract and a usage policy.
2. Ask the police department for its ALPR policy: how long reads are kept, who can search them and which agencies they’re shared with.
3. File a public records request if the policy isn’t published. Most states have a standard form.
4. Check state law. A few states limit how ALPR data can be used or how long it can be kept; many have no specific rules.

Where NitoPath’s map comes from

Camera locations come from OpenStreetMap, where volunteers add them, many through the DeFlock project. The map is never complete: a route with no known cameras can still pass ones nobody has mapped yet. If you know of one that’s missing, you can add it on DeFlock or report it from the NitoPath app.

Learn more

• Automated License Plate Readers, Electronic Frontier Foundation’s Street Level Surveillance guide
• DeFlock, the community map of license plate readers
• OpenStreetMap wiki: surveillance:type=ALPR, how cameras are recorded on the map