Do License Plate Readers Violate the Fourth Amendment?

Our Take

Credit to the Chicago Justice Project for pulling Professor Steven Keener into a conversation most local news won't touch: whether the constitutional guardrails written for door-to-door searches even make sense in an era of networked cameras clocking every car, every block, every day. Keener's framing matters because the legal fight over ALPRs isn't really about any single camera catching any single plate. It's about aggregation — the mosaic of your movements that emerges once thousands of Flock nodes are stitched together into a searchable database of where you go, when, and how often.

That's precisely the theory the Supreme Court endorsed in Carpenter v. United States when it ruled that long-term cell-site tracking required a warrant, even though no single data point seemed sensitive on its own. ALPR networks are arguably a more aggressive version of the same problem: no phone company subpoena needed, just cameras owned by your own city government, often running with minimal audit trails, vague retention policies, and no warrant requirement at all. Keener's research into the geography of Flock's rollout is a reminder that these systems aren't distributed evenly or accountably — they cluster where police departments and vendors decide, not where residents vote on it.

We keep saying it because it keeps being true: this fight will be won or lost on whether ordinary people know these cameras exist and push back before the network hardens into infrastructure. Check our map to see what's already watching your commute, and hit up our take-action page if you want to push your city council to ask the questions Keener is asking academically — before a court has to.