Amendment 4

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.

This Information from: http://legal-dictionary.thefreedictionary.com/Amendment+4

This amendment is important so that people feel they have privacy against the government coming onto or into their property and going though all of their belongings.