Exigent circumstance in United States law

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.

In the criminal procedure context, exigent circumstance means the following:

An emergency situation requiring swift action to prevent imminent danger to life or serious damage to property, or to forestall the imminent escape of a suspect, or destruction of evidence. There is no ready litmus test for determining whether such circumstances exist, and in each case the extraordinary situation must be measured by the facts known by officials.

Those circumstances that would cause a reasonable person to believe that entry (or other relevant prompt action) was necessary to prevent physical harm to the officers or other persons, the destruction of relevant evidence, the escape of a suspect, or some other consequence improperly frustrating legitimate law enforcement efforts.

Exigent circumstances may make a warrantless search constitutional if probable cause exists. The existence of exigent circumstances is a mixed question of law and fact. There is no absolute test for determining if exigent circumstances exist, but general factors have been identified, which include clear evidence of probable cause; the seriousness of the offense and likelihood of destruction of evidence; limitations on the search to minimize the intrusion only to preventing destruction of evidence; and clear indications of exigency.

Exigency may be determined by degree of urgency involved, amount of time needed to get a search warrant, whether evidence is about to be removed or destroyed, danger at the site, knowledge of the suspect that police are on the trail, and/or ready destructibility of the evidence. In determining the time necessary to obtain a warrant, a telephonic warrant should be considered. As electronic data may be altered or eradicated in seconds, in a factually compelling case, the doctrine of exigent circumstances will support a warrantless seizure.

...
Wikipedia