Which of the following best defines "unreasonable searches"?

Unreasonable searches are defined as those that take place without the necessary justification, such as probable cause or a valid warrant. The Fourth Amendment of the United States Constitution protects individuals from such intrusions, establishing that a search must be reasonable to be permissible under the law.

In this context, a search lacking probable cause or a warrant is considered a violation of a person's reasonable expectation of privacy. Probable cause requires a reasonable belief that evidence of a crime will be found in the location being searched, and a warrant is an official document that grants law enforcement the authority to conduct a search. This protection ensures that individuals are not subjected to arbitrary or capricious searches by the government.

Having a warrant, as referenced in other choices, generally signifies that a search is reasonable. However, not all searches conducted without a warrant are unreasonable—exigent circumstances or exceptions may apply. The smoothness of a search or its suggestion by the public has no bearing on its legality concerning the Fourth Amendment. Thus, searches that lack probable cause or a warrant clearly fall under the definition of "unreasonable searches."