Your Right to Privacy Doesn't Disappear When You're in Public

This piece analyzes the legal and practical limits of privacy in public, tracing how Supreme Court decisions have narrowed a simple slogan - “no reasonable expectation of privacy in public” - into a more complex rule. It notes that police cannot stop and question people at will without reasonable suspicion, then contrasts landmark cases: United States v. Knotts (1983), where a radio transmitter in a chloroform container tracked a suspect for hours and the Court found no Fourth Amendment violation; United States v. Jones (2012), where a monthlong warrantless GPS tracking of a vehicle was treated as a search because of both trespass and the revealing nature of long-term location data; Carpenter v. United States (2018), which held that people have a reasonable expectation of privacy in the “whole of physical movements” reflected in cell-site records; and Chatrie (2026), which extended that logic to Google location history.

The discussion connects those precedents to modern automated license plate reader (ALPR) systems like Flock Safety, arguing that mass, cheap, persistent location collection can reveal intimate patterns, enable retrospective tracking before any suspicion, and therefore trigger Fourth Amendment protection. Multiple lawsuits challenging warrantless ALPR use are underway, and courts are still developing rules, but the clear takeaway is that Fourth Amendment rights do not evaporate simply because someone is physically in public.