Every ping a phone sends is a digital breadcrumb - tracing where you sleep, work, worship, and wander. In Carpenter v. U.S., the Supreme Court confronted a question at the heart of modern privacy: do those invisible trails belong to you, or are they fair game for the government without a warrant?
This case examines whether the government’s warrantless collection of 127 days of cell-site location information (CSLI) - data that tracks a person’s movements through cell towers - violates the 4th Amendment’s protection against unreasonable searches. The case underscores growing concerns overlaw enforcement’s use of digital location data without warrants, raising critical questions about privacy in the modern era.
Following the oral argument held on November 29, 2017, the key highlights and lowlights of each side can be summarized as follows:
Wessler argued that obtaining CSLI constitutes a 4th Amendment search, as it reveals a detailed, continuous record of a person’s movements. He emphasized that the data is not voluntarily shared and, drawing on Riley and Jones, that pre-digital precedents must adapt to modern technology. When pressed on how to gauge the sensitivity of cell-site location tracking, Wessler argued that, like the GPS monitoring deemed a 4th Amendment search in U.S., v. Jones, CSLI reveals detailed, long-term movements and thus requires a warrant - underscoring that Jones marked a shift toward recognizing a “reasonable expectation of privacy” in such pervasive surveillance. Wessler also contended that modern technology enabling indefinite electronic tracking makes surveillance far more intrusive than in Smith
and Miller, blurring when government access becomes a 4th Amendment “search” requiring a warrant. He added that even “incidental access” can trigger constitutional protection under Katz and Riley, as digital data’s scope and sensitivity demand stronger privacy safeguards.
Wessler, however, struggled to define clear limits (e.g. what duration of tracking counts as “long-term). Additionally, he faced skepticism about whether people truly expect location privacy when cell phones are public tools.
On the other hand, Dreeben argued that CSLI qualifies as business records under the principles established in Smith and Miller, because users voluntarily share their data with carriers. Under this view, the third-party doctrine applies, and law enforcement may access CSLI without a warrant, as these records are generated by providers rather than through direct government tracking.
Dreeben argued that business records - like financial transactions or call logs - are not private when voluntarily shared with third parties, as affirmed in Smith and Miller, meaning no warrant is required. He added that judicial oversight under the Stored Communications Act, through §2703(d) orders, ensures law enforcement access to electronic records remains limited, justified, and consistent with 4th Amendment standards.
When questioned whether third-party access eliminates all privacy - echoing concerns over colonial “writs of assistance” - Breener conceded that modern surveillance precision may challenge this view. Still, under Smith, Miller, and the Katz framework, individuals who voluntarily share data with providers have limited 4th Amendment protection, though Jones suggests property-based privacy interests may still warrant consideration.
The Court grappled with the clash between enduring privacy expectations and the vast reach of modern technology, debating whether traditional doctrines like the third-party rule remain viable amid near-constant digital tracking. Ultimately, the Justices recognized a reasonable expectation of privacy in individuals’ digital footprints, signaling a need to adapt 4th Amendment protections to the realities of the digital age.
In arguing this case, I would clarify the rule with a clear threshold - such as defining tracking beyond seven days as a search - emphasize that users do not voluntarily share location data like in Smith or Miller and adopt a property-based framing aligned with Justice Gorsuch. I would also illustrate the real-world harms of warrantless access and counter the government’s business-records argument by stressing that such data is co-created through users’ physical movements.