Generally, an emergency, a pressing necessity, or a set of circumstances requiring immediate attention or swift action. In the criminal procedure context, exigent circumstances means:
United States v. McConney, 728 F.2d 1195, 1199 (9th Cir.), cert. denied, 469 U.S. 824 (1984): "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. United States v. Anderson, 154 F. 3d 1225 (10th Cir, 1998) cert. denied 119 S. Ct. 2048 (1999) (citations omitted). There is no absolute test for determining if exigent circumstances exist, but general factors have been identified. These 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 warrant; whether evidence is about to be removed or destroyed; danger at the site; knowledge of the suspect that police are on his or her trail; and/or ready destructibility of the evidence. United States v. Reed, 935 F. 2d 641 (4th Cir.), cert. denied, 502 U.S. 960 (1991). 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.
Even in exigent circumstances, while a warrantless seizure may be permitted, a subsequent warrant to search may still be necessary. See Grosenheider, supra and United States v. David, 756 F. Supp. 1385 (D. Nev. 1991).