Fourth Amendment Search and Seizure
Rule
The Fourth Amendment prohibits unreasonable searches and seizures by government actors. A “search” occurs when the government (1) intrudes on a constitutionally protected area for the purpose of obtaining information (trespass/property theory), or (2) violates a person’s reasonable expectation of privacy (Katz theory). Warrantless searches are presumptively unreasonable; the government bears the burden of showing an exception applies.
Elements / Requirements
Threshold: Government Action
The Fourth Amendment applies only to government actors (police, federal agents, public school officials). Private searches generally fall outside its scope.
Step 1: Was There a “Search”?
Two independent theories:
A. Katz REP Test (Katz v. United States, 1967)
- Defendant had a subjective expectation of privacy in the area/item searched
- Society recognizes that expectation as objectively reasonable
B. Trespass/Property Theory (United States v. Jones, 2012)
- Physical intrusion onto a constitutionally protected area (persons, houses, papers, effects) for the purpose of obtaining information constitutes a search, regardless of whether any REP is violated
Step 2: Was There a Valid Warrant?
A warrant must:
- Be supported by probable cause (fair probability that evidence of a crime will be found)
- Be issued by a neutral and detached magistrate
- Describe with particularity the place to be searched and items to be seized
Step 3: If No Warrant — Does an Exception Apply?
See Warrant Requirement.
Exceptions
- Exigent circumstances (emergency, hot pursuit, destruction of evidence)
- Search incident to lawful arrest (Chimel — area within immediate control; NOT cell phones, Riley)
- Automobile exception (Ross — probable cause to search the car)
- Plain view (Horton — lawfully present, incriminating character immediately apparent)
- Consent (voluntarily given; third-party consent issues)
- Inventory search
- Special needs / administrative searches
- Terry stop-and-frisk (reasonable articulable suspicion, not probable cause)
Policy
The Fourth Amendment balances individual privacy against the government’s law enforcement interest. The warrant requirement channels police conduct through neutral magistrates, reducing the risk of arbitrary searches. The exclusionary rule (Mapp v. Ohio) deters police misconduct by suppressing illegally obtained evidence.
Key Cases
- Katz v. United States — wiretap of phone booth is a search; establishes REP test
- United States v. Jones — attaching GPS tracker to car is a Fourth Amendment search (trespass theory)
- Riley v. California — cell phone search incident to arrest requires a warrant; digital data is categorically different
- United States v. Carpenter — government acquisition of 7+ days of CSLI requires a warrant; third-party doctrine does not apply to comprehensive digital location records
- Byrd v. United States — unauthorized driver of a rental car has a legitimate expectation of privacy sufficient to challenge a search
- Katz v. United States — foundational REP test
- Smith v. Maryland — pen register data voluntarily conveyed to phone company; no REP (third-party doctrine)
- United States v. Miller — bank records voluntarily conveyed; no REP