Katz v. United States: The Right to Privacy in a Phone Booth

The Third Party Doctrine is a US legal principle stating that when individuals voluntarily share personal information with third parties such as banks, phone companies, or internet service providers, they forfeit their reasonable expectation of privacy in that information; this doctrine was established through landmark Supreme Court cases including United States v. Miller (financial records) and Smith v. Maryland (phone call records), though recent cases like Carpenter v. United States have acknowledged the unique sensitivity of certain digital data while still reinforcing the core principle that shared information generally loses its Fourth Amendment privacy protection.

The third-party doctrine originated from US v. Miller in 1976, a case involving financial information. Miller was accused of running a distillery without paying taxes, and the government obtained his bank records (bank statements, cleared checks) from the bank without a warrant. Miller challenged this, arguing these were his papers. The court ruled that bank records belong to the banks, not the customers, establishing that information shared with third parties is no longer protected by the Fourth Amendment.

The third party doctrine that ICE relies on to avoid warrants was created decades ago in cases like United States v. Miller and Smith v. Maryland when sharing information with third parties meant limited disclosure for specific purposes and when technology didn't enable third parties to collect comprehensive records of entire life. Courts ruled that individuals don't have reasonable expectation of privacy in information voluntarily shared with third parties because they assume risk that third parties might disclose information to government. But this doctrine made sense only in world where sharing information with bank meant bank knew about specific transactions, where sharing with phone company meant phone company knew numbers dialed but not content of conversations, and where third parties held limited information about limited aspects of life that individuals consciously chose to share for specific purposes.

The Third Party Doctrine evolved from secret agent cases involving criminals to apply to ordinary citizens sharing information with banks and phone companies. In Smith v. Maryland and Miller v. U.S. (1970s), the Supreme Court held that because bank records and phone metadata were held by third parties, there was no reasonable expectation of privacy, allowing warrantless government acquisition. Critics argue this improperly transferred doctrine from criminal contexts to innocent citizens, as contract law recognizes agreements but the Fourth Amendment does not. The doctrine's reliance on whether acts are legal or illegal creates problems since investigators don't know beforehand whether information relates to lawful or unlawful conduct.

In Carpenter v. United States (2018), the U.S. Supreme Court ruled that government acquisition of historical cell-site location information (CSLI) constitutes a Fourth Amendment search requiring a warrant supported by probable cause, rejecting the third-party doctrine's application to CSLI due to the unique nature of cell phone location records and the pervasive role of cell phones in daily life, which creates a reasonable expectation of privacy in one's physical movements; this decision established that administrative subpoenas alone are insufficient for obtaining such sensitive location data, thereby raising the constitutional standard above the lower 'reasonable grounds' threshold found in the Stored Communications Act.

This segment analyzes the Supreme Court's Carpenter ruling establishing privacy rights in digital location data: (1) Cell site location information (CSLI) provides all-encompassing records of personal movements over time; (2) CSLI is collected passively without affirmative user action beyond powering the device; (3) CSLI is distinguishable from third-party doctrine cases (Miller, Smith) because of its pervasiveness and detailed nature; (4) Location history data differs from CSLI because users must opt-in and can revoke consent; (5) Location history is more akin to bank records where no reasonable expectation of privacy exists.

In Carpenter v. United States (2018), the Supreme Court ruled that collecting long-term cell phone location history constitutes a search under the Fourth Amendment requiring a warrant. Chief Justice Roberts wrote that there is a legitimate expectation of privacy in the record of physical movements captured through a person's cell phone, and tracking movement through cell signals is an invasion of that expectation. This ruling established that historical cell phone location data requires judicial approval before law enforcement can obtain it.

The 2018 Carpenter v. United States Supreme Court decision established that location data differs fundamentally from other third-party information because of what it reveals. Over time, individual data points form detailed maps of a person's life—including where they sleep, work, worship, seek medical care, and associate with others. The court recognized that the third party doctrine does not cleanly apply to location tracking because its scale and sensitivity change the constitutional analysis, shifting the question from whether data was shared to what the data reveals. This ruling creates tension with practices where governments purchase functionally equivalent data through commercial brokers rather than obtaining warrants.

The Fourth Amendment protects individuals' persons, extending beyond physical bodies to intangible aspects subject to surveillance. United States v. Jones established that freedom from surveillance underpins Fourth Amendment protections, meaning the person extends to movements and other aspects of personal identity. Whether government conduct constitutes a search depends on the scale and quality of information obtained—brief tracking of movements is not a search, but extended constant monitoring might be (United States v. Knotts). Kyllo v. United States distinguished visual observation of exterior from thermal imaging revealing heat patterns inside. Aggregated location data over extended periods can reveal comprehensive pictures of private life, transforming minimally revealing data points into highly intrusive information about personal identity.

In U.S. v. Jones, the Supreme Court unanimously ruled that attaching a GPS tracking device to a vehicle and monitoring its movements constitutes a Fourth Amendment search, because the physical invasion of property itself violates constitutional protections, regardless of whether the individual has a reasonable expectation of privacy in their public movements.

Three landmark cases establish Fourth Amendment standards for technology: (1) Katz v. United States (1967) established the 'reasonable expectation of privacy' test requiring both subjective expectation and objective societal recognition; (2) Kyllo v. United States (2001) ruled thermal imaging from a public street constitutes a search requiring a warrant, even without physical trespass; (3) United States v. Jones (2012) ruled GPS tracking constitutes a search when it involves physical trespass on private property. California v. Cerrullo (1986) ruled aerial observation from 1,000 feet over a home with privacy fences was not a search because society does not recognize privacy expectations in areas exposed to public observation. Florida v. Riley (1989) ruled helicopter observation at 400 feet was not a search because helicopters are routine and the observation didn't interfere with normal property use.

Courts have struggled to apply Fourth Amendment principles to technology-enhanced surveillance. Kyllo v. United States (2001) held thermal imaging of homes constitutes a search, emphasizing that technology unavailable to the public requires warrants. United States v. Jones (2012) required warrants for GPS tracking devices, with a shadow majority noting the invasiveness of aggregated data. These cases reflect the Court's ongoing effort to reconcile traditional Fourth Amendment principles with modern surveillance capabilities, setting the stage for Carpenter.

Katz v. United States (1967) definitively replaced trespass tests with the reasonable expectation of privacy standard, holding that electronic eavesdropping violates privacy even without physical intrusion. United States v. Jones (2012) addressed GPS tracking devices attached to vehicles, with the Supreme Court holding that such attachment constitutes a search. The majority focused on trespassory aspects of placing devices on vehicle undercarriages, while concurring opinions expressed concern that this approach might shift back toward property-centric testing. Carpenter v. United States (2018) established that historical cell site location information (CSLI) constitutes a search requiring a warrant based on probable cause. The Court held that CSLI presents greater privacy concerns than GPS tracking because it allows the government to travel back in time and retrace a person's whereabouts subject only to 5-year retention policies by carriers.