Katz V. United States Privacy Expectations Case Study
1. Katz v. United States, 389 U.S. 347 (1967)
Facts
Charles Katz was convicted based on evidence obtained by FBI agents who had placed an electronic listening device on the outside of a public phone booth to listen to his conversations without a warrant.
Legal Issue
Does the Fourth Amendment protect conversations in a public phone booth from warrantless wiretapping?
Decision
The Supreme Court ruled 7-1 in favor of Katz, holding that the Fourth Amendment protects people, not places, and established the "reasonable expectation of privacy" test.
Significance
Introduced the two-prong test for privacy:
The individual has exhibited an actual (subjective) expectation of privacy.
The expectation is one that society is prepared to recognize as reasonable.
This case shifted Fourth Amendment analysis from property-based to privacy-based.
2. Smith v. Maryland, 442 U.S. 735 (1979)
Facts
The police used a pen register to record numbers dialed from Smith’s phone without a warrant.
Legal Issue
Does installing and using a pen register constitute a “search” under the Fourth Amendment?
Decision
The Court ruled that it does not constitute a search because Smith had no reasonable expectation of privacy in the numbers he dialed, which are voluntarily shared with the phone company.
Significance
Established the third-party doctrine: information voluntarily given to third parties (like phone companies) is not protected by the Fourth Amendment.
This limited the scope of Katz in certain contexts.
3. California v. Ciraolo, 476 U.S. 207 (1986)
Facts
Police flew over Ciraolo’s backyard and observed marijuana plants without a warrant.
Legal Issue
Does aerial surveillance of a fenced backyard without a warrant violate the Fourth Amendment?
Decision
The Court held that it does not, reasoning that the public airspace is accessible and the surveillance did not violate a reasonable expectation of privacy.
Significance
Highlighted limits to privacy expectations in areas exposed to public view.
Clarified that privacy expectations depend on the nature of exposure to the public.
4. United States v. Jones, 565 U.S. 400 (2012)
Facts
The FBI attached a GPS tracking device to Jones’s car without a valid warrant and tracked his movements for 28 days.
Legal Issue
Does installing a GPS tracking device on a vehicle and monitoring it constitute a search under the Fourth Amendment?
Decision
The Court unanimously ruled that this is a search and requires a warrant, relying on the property-based approach and rejecting a narrow focus on privacy expectations alone.
Significance
Revived the property-based approach alongside the privacy expectation test.
Recognized that prolonged surveillance implicates privacy concerns beyond traditional property concepts.
5. Carpenter v. United States, 585 U.S. ___ (2018)
Facts
Police obtained months of cell-site location data (CSLI) from Carpenter’s wireless carrier without a warrant.
Legal Issue
Does the government need a warrant to access historical CSLI from a third party?
Decision
The Court ruled 5-4 that accessing CSLI is a search under the Fourth Amendment, requiring a warrant, because individuals have a reasonable expectation of privacy in their physical movements.
Significance
Limited the third-party doctrine established in Smith v. Maryland.
Expanded Katz’s reasonable expectation of privacy to digital data held by third parties.
6. Florida v. Jardines, 569 U.S. 1 (2013)
Facts
Police brought a drug-sniffing dog onto Jardines’s front porch without a warrant and detected drugs, leading to a search warrant.
Legal Issue
Does bringing a drug-sniffing dog onto a private porch constitute a search under the Fourth Amendment?
Decision
The Court held that it is a search, and a warrant is required, because the front porch is part of the home’s curtilage and protected by privacy expectations.
Significance
Affirmed privacy protections for home and curtilage against advances in law enforcement technology.
Reinforced Katz’s emphasis on societal privacy expectations.
Summary Table of Key Cases
| Case | Year | Key Holding | Privacy Principle |
|---|---|---|---|
| Katz v. United States | 1967 | Established “reasonable expectation of privacy” test | Privacy expectations over physical property |
| Smith v. Maryland | 1979 | No warrant needed for pen register data | Third-party doctrine limits privacy |
| California v. Ciraolo | 1986 | Aerial surveillance not a search | Limits on privacy in exposed areas |
| United States v. Jones | 2012 | GPS tracking = search; warrant needed | Property rights revived |
| Carpenter v. United States | 2018 | Warrant needed for CSLI | Limits third-party doctrine for digital data |
| Florida v. Jardines | 2013 | Drug dog on porch = search; warrant needed | Privacy in home curtilage protected |
Conclusion
Katz v. United States revolutionized Fourth Amendment law by focusing on privacy expectations rather than physical trespass. Over the years, the Supreme Court has both expanded and limited this principle through cases involving new technologies and changing societal norms.
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