HumenhukCIPP/US Study Guide
Chapter 13: Privacy Issues in Civil Litigation and Government Investigations

Fourth Amendment Limits on Law Enforcement Searches

Reviewed by Victor Humenhuk. Published . Reviewed .

The Fourth Amendment bars unreasonable searches; warrants need probable cause, particularity, and a neutral magistrate. Katz created the reasonable expectation of privacy test, while the in-public and third-party doctrines limit it. The exclusionary rule suppresses evidence obtained unlawfully.

How this supports CIPP/US study

Use this lesson to identify the disclosure, workplace or cross-border rule that changes the result in a fact pattern. Continue with the CIPP/US study plan.

The Fourth Amendment bans unreasonable searches and seizures. Warrants require probable cause, must be supported by specific testimony, approved by a neutral magistrate, and describe the place with particularity (no general warrants). The Exclusionary rule lets defendants exclude unlawfully gathered evidence, generating extensive case law.

Key Fourth Amendment cases
Case (year)Holding
Olmstead (1928)No warrant for wiretaps on wires outside the building (later overruled); Brandeis dissent: 'right to be let alone'
Katz (1967)Overruled Olmstead; warrant needed for phone-booth bug; established reasonable expectation of privacy test
Jones (2012)Warrant needed for month-long GPS tracking; trespass theory, with justices questioning third-party/in-public doctrines
Riley (2014)Warrant needed to search a cellphone's contents (quantitatively and qualitatively different from a physical container)
Carpenter (2018)Warrant needed for cell site location information, narrowing the third-party doctrine
In-public and third-party exceptions

Under Third-party doctrine, information voluntarily handed to a bank or phone company loses Fourth Amendment protection - so companies are generally permitted under the Constitution to turn over customer and employee records (though statutes may still restrict it). Carpenter narrowed this for cell site location information.

Key terms - quick answers

What is “Fourth Amendment”?
Constitutional protection against unreasonable searches and seizures, requiring warrants on probable cause, supported by oath, particularly describing the place to be searched.
What is “Reasonable expectation of privacy test”?
From Katz: a person must show an actual (subjective) expectation of privacy that society is prepared to recognize as reasonable.
What is “Third-party doctrine”?
The rule that information voluntarily given to a third party (e.g. bank or phone company) loses Fourth Amendment protection, so a warrant is not required to obtain it.
What is “Exclusionary rule”?
Evidence gathered in violation of the Fourth Amendment may be excluded from a criminal trial.

Sources and study method

This independent lesson uses active recall, spaced retrieval and scenario practice. Read the full study method.