Exigent Circumstances refer to situations that demands unusual or immediate action and this allows people to circumvent usual procedures. In other words emergency conditions. The circumstances are such that it would cause a reasonable person to believe that prompt action is necessary to prevent physical harm to the officers. For example when a neighbor breaks through a window of a burning house to save someone inside.
These are situations in which a police officer can take immediate action to effectively make an arrest, search, or seizure for which probable cause exists. This can be done without first obtaining a warrant. The federal 'knock and announce' statute, 18 U.S.C. S 3109 requires police officers to knock, announce and be refused entry before they break into a residence. However, exigent circumstances excuse noncompliance.
Exigent circumstances are said to exist when
(1) a person's life or safety is threatened
(2) a suspect's escape is imminent, or
(3) evidence is about to be removed or destroyed.
This is also termed as emergency circumstances or special circumstances.