Exigent circumstances - "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 the suspect, or some other consequence improperly frustrating legitimate law enforcement efforts."
In Missouri v. McNeely (2013), the Supreme Court clarified, "A variety of circumstances may give rise to an exigency sufficient to justify a warrantless search, including law enforcement's need to provide emergency assistance to an occupant of a home . . . engage in “hot pursuit” of a fleeing suspect . . . or enter a burning building to put out a fire and investigate its cause."
Courts will typically look at the time when the officer makes the warrantless search or seizure to evaluate whether at that point in time a reasonable officer at the scene would believe it is urgent to act and impractical to secure a warrant. Courts may also consider whether the facts suggested that the suspect was armed and planning to escape, whether a reasonable police officer would believe his safety or others’ safety was threatened, and whether there was a serious crime involved.