No-knock warrants authorize police to force entry into a home without first knocking and announcing their presence. Courts have generally required some heightened showing — usually that announcement would let suspects destroy evidence, endanger officers, or flee. The Supreme Court has held that the knock-and-announce rule is part of the Fourth Amendment, but suppression of evidence is generally not the remedy for violations.
Use of no-knock warrants expanded sharply during the war on drugs. Several high-profile deaths during no-knock or "quick-knock" raids — most notably Breonna Taylor in 2020 — prompted federal and state restrictions. The Justice Department now restricts no-knock entries by federal agents to limited circumstances, and several states and cities have banned or sharply limited them.
Debate centers on when, if ever, dynamic surprise entries are justified, what evidentiary threshold should apply, and how to weigh officer safety against the safety of occupants and bystanders.