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


Another Amendment that people sometimes incorrectly cite.

For example, if you CHOOSE to fly, you have lost all reasonable expectations of privacy; so claims that the TSA searches are unconstitutional are invalid.