Which of the following is an exception to the need for a search warrant?

The correct choice is based on the legal principle of "search incident to arrest," which allows law enforcement officers to conduct a search of an individual and their immediate surroundings without a warrant when that individual is being arrested. This exception is rooted in the need for officer safety and the preservation of evidence. When an officer makes an arrest, they may search the arrestee and the area within their immediate control to ensure that no weapons or contraband can be accessed or destroyed.

This principle is established in various court cases, including the landmark decision in Chimel v. California, which clarified the extent to which searches can be conducted without a warrant in connection with an arrest. The rationale is that such searches help protect the safety of officers and others, as well as prevent evidence from being lost or destroyed.

The other options are not recognized exceptions in the same way. For instance, waiting for a suspect to leave does not inherently justify a warrantless search. Searching without probable cause contradicts foundational Fourth Amendment principles, and investigating a complaint generally requires officers to establish probable cause before conducting a search, unless other exceptions apply. Therefore, "search incident to arrest" stands out as a clear and established exception to the warrant requirement in constitutional law.