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.
In the United States, the Fourth Amendment remains a powerful protection that its citizens use to guard against abuse of police power. Often a criminal trial will depend on a particular piece of evidence. If this evidence is gathered by the police in a way that violates the Fourth Amendment, then the judge will exclude the evidence from the trial. This often leads to the acquittal of the defendant. The effect is to provide a strong incentive to every police officer in the United States to understand and apply the search and seizure rules of the Fourth Amendment.
The courts' interpretation of the Fourth Amendment changes over time, and the rules on the exclusion of evidence often seem subjective and dependent on the circumstances. At one extreme, evidence is clearly admissible if it is in clear sight of a policeman walking down the street. At the other extreme, evidence is clearly inadmissible if a policeman opens the door of a random house, searches it without a warrant or other legal authorization, and seizes the evidence. Between these two extremes, one can imagine countless scenarios which are less clear-cut, so the courts have adopted various standards of "probable cause" and "reasonable suspicion" in deciding whether a particular search or seizure violates the Fourth Amendment.Analysis
