The Fourth Amendment
This is why I think reading the Bill of Rights occasionally is kind of important. First, read this:
Amendment IV: 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.
And then watch this: The NSA and the 4th Amendment
It’s important that at least some of us actually occasionally read and understand the founding documents. Because we can’t assume that people in power necessarily will.