The major evil against which the Fourth Amendment protects is the physical entry of the home. The Fourth Amendment requires that searches of the home be reasonable. This reasonableness requirement generally requires that police obtain a warrant based upon a judicial determination of probable cause prior to entering a home. The Fourth Amendment prohibition against entering a home without a warrant applies equally whether the police enter a home to conduct a search or seizure or for some other purpose. There are, however, a few well-defined and carefully circumstances in which a warrant will not be required.
Exigent Circumstances: One such exception is exigent circumstances: Exigent circumstances are situations where real immediate and serious consequences will certainly occur if a police officer postpones action to obtain a warrant. The following situations may give rise to exigent circumstances: 1) hot pursuit of a fleeing felon; 2) fear of imminent destruction of evidence; 3) the need to prevent a suspect’s escape; and 4) a risk of danger to the police or others. The Fourth Amendment also does not stop police officers from making warrantless entries and searches when they reasonably believe that a person inside is in need of immediate aid. The “risk of danger exigency” most frequently justifies warrantless entries in cases where law enforcement is acting in something other than a traditional law enforcement capacity. The “risk of danger” exigency, however, only applies in situations involving the need to protect or preserve life or avoid serious injury either of police officers themselves or of others.
Automobile Exception: With regards to automobile searches, under the automobile exception, a warrantless search of a vehicle is justified if the police have probable cause to believe it contains contraband or evidence of a crime.
Probable Cause: Probable cause exists when the information on which the warrant is based is such that a reasonable person would believe that what is being sought will be found in the location to be searched. Probable cause must attach to each place to be searched.
Particularity: Also, when obtaining a search warrant, the Fourth Amendment requires that it particularly describe the place to be searched. But the description of the place to be searched does not need to be perfect.