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Chapter 3 · The Fourth Amendment
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From the page before
What does a valid warrant have to describe?
The answer: The specific place to be searched and the things to be seized
Why: The warrant must name the place and the things. That is what rules out the general warrant, which is the grievance the amendment was written to answer.
Which standard is required for an arrest?
The answer: Probable cause
Why: Reasonable suspicion is enough for a brief stop. Probable cause is the higher bar. It is needed for an arrest and for most warrants.
Officers, judges and news reports use these two terms with care. The gap between them decides cases. It is worth learning which one you are hearing.
Your phone
The Supreme Court has held that police usually need a warrant to look inside a phone taken during an arrest. They usually need one to get old cell-site records that show where a phone has been.
The reason is the same in both. A phone holds far more, and far more private, than a wallet or a pocket.
In Chatrie v. United States, No. 25-112, decided June 29, 2026, the Court went further. Police had asked Google which phones were near a crime scene at a given time. That is called a geofence warrant. The Court held, 5 to 4, that getting that location history is a search under the Fourth Amendment, because a person has a reasonable expectation of privacy in records of where their phone has been. Justice Kagan wrote the opinion.
The Court did not decide whether that search was reasonable. It did not decide whether the evidence can still be used. It sent those questions back to the lower court. We say so plainly, because they are open.
The exclusionary rule
Evidence from an unconstitutional search usually cannot be used against you.
That rule is the engine. Without it the amendment would be a preference rather than a rule, because breaking it would cost nothing.
Before you turn the page
Police generally need a warrant to search the contents of a mobile phone taken during an arrest. Why?
Trying to recall a thing before you read it again is what makes it stick. That is why the question is here.
Nothing is scored. Nothing is saved. No one sees your answer, and there is no account to make.