Image Credits: @riiyad on Unsplash (Unsplash License)

---

In an era of digitalization, privacy is becoming increasingly susceptible to government encroachment. It is both jeopardized and blurred by digital surveillance technologies which are unstoppably proliferating and advancing. One aspect that must be further considered is how to define the scope of privacy and the reasonableness of privacy expectation, which has been dealt with in numerous cases. This can be seen with Carpenter v. United States, in which a robbery suspect, Timothy Ivory Carpenter was sentenced to 1,395 months’ imprisonment, and moved to suppress cell site location information (CSLI) evidence. Carpenter argued CSLI, a record of cellphone’s locations, shall be obtained only with a warrant. Carpenter v. United States represents debates over the judicial reinterpretation of the Fourth Amendment which protects privacy from unreasonable searches. This landmark case sheds new light on how to update and modify the Fourth Amendment rules by which privacy is defined and protected, accordingly as technologies evolve.

Historical Overview 

Property-oriented interpretation

The Fourth Amendment protects “the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures”. The initial interpretive method of the Fourth Amendment was property-oriented. Privacy rights were tightly fused with property concepts. This interpretation can be seen under Ex parte Jackson in which the Amendment was seen only applicable to properties resembling a sealed container. Such understanding can be advanced with Olmstead v. United States. In this case, Chief Justice Taft suggested privacy consists solely in specifically enumerated “material things” in the Amendment; hence the warrantless wire-tapping “without trespass upon any property” was held constitutional. Moreover, “possessory interests” in property were emphasized in United States v. Jacobsen, to be further shown in United States v. Lyons which ruled that the seizure of stolen disks was constitutional. These cases demonstrated that privacy only pertained to physical objects in a segregated spatial area under individual’s ownership. Property-space interpretation of the Fourth Amendment dominated until Katz v. United States.

Expectation-centric interpretation 

The interpretive approach of the Fourth Amendment after Katz v. United States, was expectation-centric. In this case, the warrantless recording of public telephone conversation was considered unconstitutional. The public telephone, neither owned by the petitioner nor an independent spatial sphere, could hardly be construed as a constitutionally protected area. However, the court asserted, “the Fourth Amendment protects people, not places,” deconstructing the property-space criterion for privacy and recasting it around individual-expectation criterion—the reasonable expectation of privacy became an integral part of the Fourth Amendment doctrine. 

According to Justice Harlan, the privacy expectation could be defined by a two-fold structure: subjective anticipation and societal recognition. Under this framework, once an individual intentionally exhibits an intention of hiding what she or he expects to be private, and society also recognizes this intention, the expectation will be confirmed. Conversely, if an individual publicly discloses what she or he does not expect to be private, and society also recognizes this disclosure, the expectation will be relinquished. The expectation-centric interpretation was widely adopted by the post-Katz cases. 

New challenges in digital era

With the rise of digital technologies, the privacy expectation of digital information with intangible qualities, becomes hard to be apprehended. Confirming whether an individual hides or discloses a piece of information is oftentimes difficult. Such ambiguity of the two-step Katz test is exemplified by the case of Kyllo v. United States. For example, here, the government used a thermal imager to detect infrared radiation emanating from the petitioner’s home. Here the subjective anticipation of the collected data could not be easily confirmed, because telling whether the petitioner intended to “conceal the heat escaping from his home” was tricky. In summary, the preceding cases play an important role in interpreting privacy and the Fourth Amendment. However, further clarification was needed especially in terms of the two-step Katz test of privacy expectation in digital technologies. Taking account of the precedents, Carpenter v. United States updated the Katz expectation doctrine by widening privacy expectation to some type of location data and delimiting the scope of third-party rule.

Carpenter v. United States

Background and facts

The privacy expectation in digital technologies can be further seen with Carpenter v. United States, in which a robbery suspect challenged the constitutionality of warrantless search of cell site location information (CSLI). After a series of armed robberies in Detroit, the police arrested four suspects including Timothy Ivory Carpenter. After procuring the participants’ phone numbers, the FBI gained court orders to obtain CSLI for the suspects. Essentially, CSLI is a time-stamped record of a phone’s geolocation. This record is generated and stored by the wireless carrier during the phone’s connection to surrounding cell towers. From 12,898 location points, the prosecutors produced maps placing Carpenter’s phone near four of the robberies; thus convicted Carpenter of “aiding and abetting robbery” by proving Carpenter was at the exact time and location of the robberies. However, Carpenter made a motion to suppress the CSLI-related evidence on Fourth Amendment ground, which was denied by the district court but affirmed by the Sixth Circuit. The Supreme Court approved certiorari to settle the court split.

Ruling and rationale

The court ruled that the warrantless attainment of CSLI violated the Fourth Amendment with a 5-4 majority on the grounds of privacy expectation and inapplicability of third-party rule. First, CSLI is entitled to privacy expectations. When an individual enters the public sphere, its behaviors and movements, albeit under the plain view of the society, are not disclosed in their entirety. However, the CSLI is “detailed” and “encyclopedic”, forming a perfect surveillance of every movement of an individual. As long as the phone signals keep hitting the towers, carriers are able to triangulate and pinpoint the phone’s location, thereby constantly cataloging and chronicling its holder’s physical whereabouts in both public and private spheres. Once the government accesses the carrier’s repository of CSLI, it can reconstruct a map of an individual’s presence on both spatial and temporal dimensions which manifests multiple facets of her or his personal life. What the government monitors could go far beyond what an individual willingly exposes. Therefore, CSLI shall be considered as a component of privacy expectation due to its all-encompassing nature. 

Second, CSLI protection is not undermined by third-party rule. Not only are movements recorded by CSLI not exposed to the society in their entirety, but the CSLI itself is also not voluntarily shared with the carrier. A dominant majority of the activities on a phone entail data connections to the carriers, meaning once it is operative and the user starts texting, calling, browsing, searching etc., CSLI will be generated. Disabling CSLI-transmission requires disconnecting the phone from networks and thereby immobilizing its normal function, which impinges upon the user’s participation in modern society. Moreover, there is no affirmative act prior to the phone’s powering up and functioning. CSIL is involuntarily “shared” with the third-party carrier without the user’s consent, which would not curtail the privacy expectation.

Post-Carpenter Development

A small step

While Carpenter’s holding was widely heralded as revolutionary, its limitation shall be brought to surface. It merely gave a narrow decision: only CSLI was entitled to Fourth Amendment protection. The holding was entirely predicated upon the very distinctive characteristic of CSLI. Carpenter only focused on its present CSLI issue instead of expressing a view on possible future matters. It is necessary to examine how post-Carpenter cases applied and extended Carpenter’s holding.

Broadening Carpenter’s application

Carpenter’s application can be extended to certain categories of non-CSLI location data. In Commonwealth v. Almonor, the police’s action that caused the fleeing suspect’s phone to transmit real-time GPS coordinates was ruled unconstitutional. The real-time GPS data of the phone is gathered through constant transmission of satellite signals, while the historical CSLI is collected through sporadic transmission of phone signals to cell-site towers. Nevertheless, the court asserted the former constitutes as powerful surveillance as does the latter, and therefore manipulating phones for revelation of such data with no authorization is also unreasonable. In Demo v. Kirksey, the scope of privacy expectation was further expanded to any “continuous gathering of geolocation data”. Therefore, it is reasonable to extrapolate that the data derived from Wi-fi access points, Bluetooth, beacon and other non-CSLI location data may possibly qualify Carpenter’s application. Ultimately, as long as the location data are collected by lengthy tracking of devices which follow their user everywhere, they are comprehensive and detailed enough to serve as perfect proxy for the user’s movements as is the CSLI. This perfect surveillance necessitates privacy expectation despite specific discrepancies in the scientific structures and technological sources. Nonetheless, further observation will still be needed to determine whether other non-location data, whose essence is such all-encompassing monitoring, can be governed by Carpenter.

Conclusion

The central issue of digital privacy protection is reconciling legal interpretation with technological development. However, the latter often outpaces the former. In the face of the proliferation of new surveillance technologies with distinct hallmarks, defining digital privacy remains in a state of flux and thus requires constant efforts. The key is achieving an optimum categorization, namely, properly ascribing categorial rules to miscellaneous technologies which may intrude on privacy. This categorization cannot be too discrete. Should distinctive rules be specifically created for each surveillance technology, the law will entail too many bifurcations to keep pace with technological evolvement due to a dearth of general principle, as seen in Carpenter v. United States. Neither can the categorization be too encompassing. By unifying and synthesizing rules for different technologies into one simple ready-to-apply criterion, the law will be too ambiguous to be applied, which was demonstrated in the Katz expectation test. Therefore, through both judicial opinions and congressional codification, the further protection lies in generating a comprehensive set of rules which keeps balance between specificity and coherence.