Constitution of the United States – Fourth Amendment
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.
* Unreasonable—without reason—that is, without justified cause detailed in a warrant that satisfies the above-stated requirements, issued by a judge of an independent judiciary who is constitutionally charged with viewing the request skeptically, and empowered to act as a check on the illegitimate exercise of power by officers of the executive branch of government by saying, in effect, No, sorry, you haven’t provided sufficient reason for me to authorize you to violate that person’s rights.