An exigent circumstance, in the criminal procedure law of the United States, allows law enforcement, under certain circumstances, to enter a structure without a search warrant or, if they have a "knock and announce" warrant, without knocking and waiting for refusal. It must be a situation where people are in imminent danger, evidence faces imminent destruction, or a suspect's imminent escape. Once entry is obtained, the plain view doctrine applies, allowing the seizure of any evidence or contraband discovered in the course of actions consequent upon the exigent circumstances.