What is the fouth amendment?

The Fourth Amendment to the United States Constitution is the part of the Bill of Rights which guards against unreasonable searches and seizures. It was ratified as a response to the abuse of the writ of assistance, which is a type of general search warrant, in the American Revolution. The amendment specifically requires search and arrest warrants be judicially sanctioned and supported by probable cause. Search and arrest should be limited in scope according to specific information supplied to the issuing court, usually by a law enforcement officer, who has sworn by it.

Source：http://en.wikipedia.org/wiki/Fourth_Amendment_(U.S._Constitution)