According to the 4th Amendment, which action requires a warrant?

The Fourth Amendment of the United States Constitution protects individuals from unreasonable searches and seizures and establishes the necessity of obtaining a warrant based on probable cause to conduct searches of private property. A warrant is typically required before law enforcement can search a person's home, personal belongings, or other private areas where there is a reasonable expectation of privacy.

Conducting a search of a property falls squarely within this framework, as it involves examining a place where a person has an expectation of privacy. The requirement for a warrant helps to ensure that searches are not conducted arbitrarily and that a neutral judge has evaluated the necessity of the search based on the evidence presented.

In contrast, while arresting a suspect also requires legal justification and often a warrant, there are circumstances where an arrest can be made without one, such as in the case of witnessing a crime in progress. Detaining a person for questioning does not require a warrant, as police officers frequently stop individuals for investigation without a warrant based on reasonable suspicion. Issuing a subpoena, which compels a person to attend court or produce documents, is governed by different legal standards and does not necessitate the protections afforded by the Fourth Amendment.