The Fourth Amendment to the United States Constitution explicitly states:
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 aforesaid provision reflects the constitutional guarantee on protecting an individual against unreasonable searches and seizures. In criminal procedure, search is taken to mean as the examination of a person's body, property or other area which a person would "reasonably be expected to consider as private" done by a law-enforcement officer in order to find evidence of a crime. Seizure, on the other hand, pertains to the act of taking possession a person's body or property by legal right or process (Black's Law Dictionary, 2004).
The Fourth Amendment, which protects one's right against unreasonable searches and seizures, shows the respect for one's privacy.
The Fourth Amendment may be invoked only against the state. It may only be applied against state actions or actions taken by government officials or at the direction of government officials. The purpose of this provision is to suppress the law-enforcement officers from conducting investigations or making arrests that are violative of one's right to privacy (Legal Dictionary, 2010).
The Fourth Amendment explicitly provides for the requirement of the existence of probable cause before a warrant (search warrant or arrest warrant) is issued. With probable cause, we refer to a reasonable belief in the existence of facts where a claim is based and in the validity of the claim itself.
Probable cause amounts to more than a bare suspicion, but less than that required to sustain conviction (Black's Law Dictionary).
In United States vs Lefkowitz (285 U.S. 452, 464), the Court held that the warrants must be issued by a judicial officer or a magistrate. This is because they pass the two tests of the validity of power of the one who will issue the warrant. The first test is that he must be neutral and detached; the second is that he must be able to determine whether probable cause exists. If the issuing party is the law enforcement officer who will conduct the search and seizure, then the first test will not be met. The person's privacy will then be left to the will of the law enforcement officer. As to the second requisite, the Court adopts a pragmatic approach in assessing the capacity to determine probable cause (FindLaw.com). In certain instances, search and seizure may be conducted even without warrant if so required by the exigencies of the situation. The search incident to an arrest, for example, is allowed even without warrant. In case of stop and frisk, the officer may also conduct a search of a person for a concealed weapon even without a warrant or probable cause. This, however, may be done only if with reasonable suspicion that the person has committed or is about to commit a crime (Black's Law Dictionary, 2004). There is also the concept of "emergency exception" or "emergency doctrine" where a police officer is allowed to conduct search even without warrant if there is probable cause and reasonable belief on the part of the officer that an immediate action is needed to protect life or property (Black's Law Dictionary).
In order to ensure that the right to privacy guaranteed by the Constitution is protected, there is what is called the exclusionary rule, where the evidence obtained in violation of the Fourth Amendment is inadmissible in evidence. Any evidence tainted with illegality cannot be used against anyone at the expense of his right to privacy.