The Fourth Amendment
Searches and warrants
Protects you from unreasonable searches and seizures and sets the standard for when police need a warrant.
Ratified 1791 · 3 minute read
Published by Quasi-Legal Institute · Report an error
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.
In plain language
What is protected
Your body, your home, your documents, and your belongings. Courts have applied “papers and effects” to modern things too: in Riley v. California (2014), the Supreme Court held that police generally need a warrant to search the data on a cell phone.
What counts as a search
The modern test comes from Katz v. United States (1967): a search occurs when the government violates a reasonable expectation of privacy. You have such an expectation in your home and in a closed bag, for instance. You generally do not have one in things you knowingly expose to the public, like a conversation held loudly on a sidewalk.
That is why a police officer looking at what is visible from a public street is usually not conducting a search, while an officer opening your backpack usually is.
Warrants, and the exceptions to them
As a general rule, a search needs a warrant based on probable cause. But courts have recognized several exceptions. The most common are consent (you agree to the search), plain view (something illegal is openly visible), emergencies where waiting would be dangerous, searches of a person during a lawful arrest, and certain searches of vehicles.
Consent matters in everyday life. If an officer asks, “Mind if I take a look?”, you are allowed to say no. If you say yes, the officer does not need a warrant.
What happens when police break the rules
Under the exclusionary rule, evidence found through an unconstitutional search generally cannot be used against you in court. The Supreme Court applied this rule to state courts in Mapp v. Ohio (1961). It exists mainly to discourage police from cutting corners, not to protect people who have broken the law.
What changes in a public school
Schools get more flexibility. In New Jersey v. T.L.O. (1985), the Court held that school officials need only reasonable suspicion, not probable cause, and no warrant, to search a student. The search must be justified at the start and reasonable in scope.
That flexibility has limits. In Safford Unified School District v. Redding (2009), the Court found that strip-searching a 13-year-old for ibuprofen was unreasonable, because the suspected violation was minor and the search was far too intrusive for it.