However, in what amounts to a permissible concession to the reasonable demands of law enforcement, the law permits the police practice of stopping for questioning any citizen who, under the given circumstances, is deemed by the police officer to be behaving suspiciously. Although the Constitution does not specifically use the term privacy, the Fourth Amendment provides protection of this right by forbidding unreasonable searches and seizures and by requiring that any search warrant be based on probable cause. Search is any governmental intrusion into a person's reasonable and justifiable expectation of privacy. It is not limited to homes, offices, buildings, or other enclosed places. All searches must be limited to the specific area and specific items described in the warrant.
General searches are unconstitutional and never legal.
There are several exceptions to the warrant requirement. They are search with consent, search incident to lawful arrest, and search under exigent circumstances. Electronic surveillance is a form of search and seizure and as such is governed by the Fourth Amendment . To obtain electronic surveillance warrant, probable cause that a person is engaging in particular communications must be established by the court, and normal investigative procedures must have been already tried. Any evidence obtained by the government in violation of the Fourth Amendment is not admissible in a criminal prosecution to prove guilt.