In the 1924 case of Carroll et al. v. United States, the U.S Supreme Court ruled that law enforcement officers do not need a warrant to search an automobile if they have probable cause to believe it contains contraband or evidence of a crime. The decision was based on the Fourth Amendment's prohibition against unreasonable searches and seizures. In this case, federal Prohibition agents stopped and searched George Carroll and John Kiro’s vehicle without a warrant but with suspicion that they were transporting illegal liquor; their suspicions proved correct when they found hidden bottles of whiskey in the car's upholstery. The defendants argued that this constituted an unlawful search under the Fourth Amendment because there was no warrant for searching their vehicle specifically, despite having obtained one previously which had expired before being executed due to lack of opportunity by authorities. However, considering automobiles' mobility nature compared to homes or offices where obtaining warrants would be feasible before conducting searches, Justice Taft delivered the court’s opinion upholding such unwarranted yet reasonable vehicular searches as constitutional exceptions.

In the dissenting opinion for Carroll et al. v. United States, Justice McReynolds expressed concern over the potential erosion of Fourth Amendment protections against unreasonable searches and seizures due to the majority's ruling. He argued that allowing warrantless vehicle searches based on probable cause could lead to abuse by law enforcement officers who might claim after-the-fact justifications for their actions. Furthermore, he contended that such a precedent would effectively nullify constitutional safeguards intended to protect citizens from arbitrary invasions of privacy and property by government officials. In his view, any exigent circumstances should be evaluated on a case-by-case basis rather than establishing an overly broad rule permitting warrantless automobile searches under all conditions where there is probable cause.