Fourth Amendment Limits on Law Enforcement Searches
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.
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.
| 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 |
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.