In Johnson v. United States (1947), the Supreme Court ruled that law enforcement officers must have a warrant to enter and search a private residence, even if they smell burning opium. The case involved Seattle police who detected the odor of burning opium coming from an apartment building. They knocked on one of the doors, and when resident Gladys Johnson opened it slightly, an officer pushed his way in without her permission or a search warrant. Inside they found drugs and arrested Ms. Johnson for illegal possession of opium. The court held that this violated her Fourth Amendment rights against unreasonable searches and seizures because there were no exigent circumstances justifying entry without a warrant - such as immediate danger or risk evidence would be destroyed before obtaining one could occur. Justice Robert H Jackson wrote: "If we are to make judicial exceptions to constitutional guarantees whenever some reasonable alternative requiring less than strict compliance has been ignored by police," he said, "we might as well abandon all attempts at guaranteeing individual liberty through written constitutions." This decision reinforced citizens' privacy rights in their homes under the Fourth Amendment.

In the dissenting opinion for Johnson v. United States, Justice Frankfurter argued that the majority's decision undermined Fourth Amendment protections against unreasonable searches and seizures. He contended that a warrantless search of a private residence was not justified merely by an officer's belief that evidence might be destroyed if they took time to secure a warrant. Instead, he suggested such exigent circumstances should only apply when there is clear evidence of imminent danger or escape risk. Furthermore, he criticized the majority for relying on testimony from officers about their subjective fears rather than objective facts to justify their actions. In his view, this approach could lead to abuses of power and erosion of constitutional rights as it gives too much discretion to law enforcement officials in determining what constitutes an emergency situation requiring immediate action without judicial oversight.