The Fourth Amendment to the Constitution protects people from illegal search and seizure: The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized. The exclusion of evidence obtained from such an illegal search, known as the exclusionary rule, is purported to sanction unconstitutional police conduct by prohibiting illegally seized evidence from being admitted into court. The state's case against a defendant is almost always harmed by the application of the rule, and thus police are deterred from violating the rights of defendants.
C. M. Stinger,
Arizona v. Evans: Adapting the Exculsionary Rule to Advancing Computer Technology,
Rich. J.L. & Tech
Available at: http://scholarship.richmond.edu/jolt/vol2/iss1/6