A plain-language field guide to the words that show up in surveillance debates — from the tech on the pole to the legal theories behind it. Bookmark it and come back.
ALPR (Automated License Plate Reader)
A camera system that photographs passing license plates, converts them to text, and logs each read with a time and location — regardless of whether anyone is suspected of a crime. See how they actually work.
Aggregation (Mosaic Theory)
The legal idea that many individually harmless data points — each plate read — combine into a revealing portrait of a person’s life that deserves privacy protection, even if any single read does not.
Carpenter v. United States
A 2018 U.S. Supreme Court decision holding that long-term tracking of a person’s location through cell-phone records requires a warrant. It’s frequently cited in arguments that mass ALPR tracking should require one too. See the legal picture.
Data Retention
How long a system stores plate reads before deleting them. It ranges from a few days to indefinitely — and in many towns there is no written policy at all.
Data-Sharing Network
Agreements that let one agency’s ALPR reads be searched by others, so a plate scanned in your town can be looked up from another state. See where your data goes.
Flock Safety
A private company that sells ALPR cameras and the searchable network behind them to police departments, HOAs, and businesses. See what Flock Safety is.
FOIA / Public Records Request
A legal request for government documents under a public-records law. One of the most effective ways to learn your town’s camera policy. See how to file one.
Geofence Search
A request for every device or vehicle present in a defined area during a window of time. Aggregated ALPR data can power a similar “who was here?” search of drivers.
Gunshot Detection
Acoustic sensors marketed alongside camera systems that claim to detect and locate gunfire. Controversial for accuracy, cost, and its role in expanding neighborhood surveillance.
Hot List
A watchlist of plate numbers that triggers a real-time alert whenever any camera in the network sees one. Powerful for stolen cars — and easy to misuse against anyone someone decides to watch.
OCR (Optical Character Recognition)
The software step that turns a photograph of a plate into machine-readable text so it can be stored and searched.
Persistent Surveillance
Continuous, always-on monitoring of everyone in an area, rather than a targeted search based on individual suspicion. It is the default mode of most ALPR deployments.
Plate Read
A single record: the plate number plus a timestamp, a location, and often a vehicle description. It is the basic unit of ALPR data.
Real-Time Crime Center
A police hub that pulls camera feeds, ALPR alerts, and other data streams into one monitoring dashboard.
Retention Limit
A policy cap on how long reads may be kept. Short, enforced limits are one of the most common and reasonable reform asks. See how to ask for one.
Third-Party Doctrine
The legal theory that information shared with a third party (such as a technology vendor) receives less privacy protection — increasingly contested as applied to modern mass surveillance.
Vehicle Fingerprint
The set of attributes a system records beyond the plate itself: make, color, body type, and distinguishing features like bumper stickers or roof racks.
Warrantless Tracking
Recording a vehicle’s movements with no warrant and no individualized suspicion — the standing default of most ALPR systems.
Now put it to use
You know the vocabulary — go find out what’s watching your own street.