The Fourth Amendment typically requires a warrant with probable cause in order to perform a search. However, there are times where the need for a search warrant does not outweigh an immediate danger. Instances where a police officer has probable cause but no time to secure a warrant from a judge is known as an exigent circumstance.

A major example of an exigent circumstance under the Fourth Amendment is the potential loss of evidence. The specific circumstance can be best exemplified with the Cupp v. Murphy case. Doris Murphy was found strangled in her home, and this led investigators to question husband Daniel Murphy at the local police station. During questioning, the investigators noticed Murphy continuing to fiddle with his fingernails. The investigators then asked Murphy for permission to get a sample underneath the fingernails. Murphy denied the request, but the investigators took a swab anyways against his objection and without a warrant.

The sample later revealed that the fingernail sample contained Doris Murphy's blood, which eventually was used as evidence in convicting Daniel Murphy of second degree murder. The Supreme Court upheld the conviction, citing that a warrant was not needed since there was a chance that Murphy would have later destroyed the evidence. The investigators had probable cause and a fear that evidence would be destroyed to complete the fingernail swab.

However, there is a limit to how far investigators or police can take evidence with a fear that it could be lost or destroyed without a warrant. In Rochin v. California, officers sent Rochin to a hospital in order to pump his stomach to retrieve two morphine pills. The Supreme Court heavily criticized the police for their actions and ruled that the procedures in garnering evidence must not be one that "shocks the conscience."

Recent cases involving the Fourth Amendment and the exigent circumstance of loss of evidence involve breathalyzers and blood alcohol tests. In Missouri v. McNeely, the Supreme Court ruled that a warrant was required to take a blood sample even with the exigent circumstance. The Supreme Court did, however, state that exceptions could be made if other factors, such as an emergency, could make the use of a blood test permissible without a warrant when testing intoxication levels. In Birchfield v. N.D. the Supreme Court ruled that a breathalyzer didn't require a warrant because there was limited contact with an individual, and the interest of protecting safety outweighed the privacy interests of the individual.

Overall, the Supreme Court has decided on the boundaries and limits on protecting public safety from drunk driving while balancing the protections under the Fourth Amendment.