In the United States v. Montoya De Hernandez case of 1984, the U.S. Supreme Court ruled that customs officials can detain incoming travelers on suspicion of smuggling contraband in their alimentary canal (stomach and intestines). The defendant, Rosa Elvira Montoya de Hernandez, was detained at Los Angeles International Airport under suspicion of being a "balloon swallower," someone who smuggles narcotics by swallowing balloons filled with drugs. After over sixteen hours of detention without producing any evidence through bowel movement, a court order was obtained for an x-ray which confirmed she had swallowed drug-filled balloons. She was subsequently arrested and charged with federal narcotics offenses. The defense argued that her Fourth Amendment rights against unreasonable searches and seizures were violated due to the length and nature of her detention before obtaining a warrant for an x-ray search. However, the Supreme Court upheld her conviction stating that reasonable suspicion based on specific facts justified temporary detention for further investigation at international borders or their functional equivalent like airports.

In the dissenting opinion for United States v. Montoya De Hernandez, Justice Brennan argued that the majority's decision failed to adequately protect individual rights against unreasonable searches and seizures as outlined in the Fourth Amendment. He contended that a reasonable suspicion should be required before detaining travelers at international borders for extended periods of time or subjecting them to intrusive body cavity searches. In this case, he believed such a standard was not met prior to detaining Ms. Montoya de Hernandez. Furthermore, he criticized the majority’s reliance on customs officials' discretion without judicial oversight as an inadequate safeguard against potential abuses of power and violations of civil liberties.