Class aptent taciti sociosqu ad litora

Proxy Tracking

  • August 12, 2017
  • Clayton Rice, K.C.

The circuits of the United States Court of Appeals have been generally consistent in this result – third party information related to the sending and routing of electronic communications does not receive constitutional protection. The third party doctrine has been moored in Fourth Amendment jurisprudence for thirty-eight years by State v Maryland, 442 US 735 (1979). But that might change.

The Supreme Court of the United States has agreed to hear argument on this question: Whether the warrantless seizure and search of historical cell phone records revealing the location and movements of a cell phone user over the course of 127 days is permitted by the Fourth Amendment. (See: Carpenter v. United States, No. 16-402). The case concerns the government’s acquisition of cell site location information (CSLI) to identify Timothy Carpenter’s whereabouts over more than four months. Carpenter was a suspect in an investigation by the police in Detroit, Michigan, into various robberies of Radio Shack and T-Mobile stores.

Carpenter moved to suppress the CSLI records before trial on the basis that the Fourth Amendment prohibits their acquisition without a warrant based on probable cause. The district court denied the motion ruling that there is no reasonable expectation of privacy in CSLI records. Their acquisition by the government did not therefore constitute a Fourth Amendment search. A jury convicted Carpenter of six robberies and firearm offences. He was sentenced to nearly 116 years imprisonment and his appeal was dismissed by the US Court of Appeals for the 6th Circuit. I previously discussed the ruling in my post titled Digital Crumbs dated May 26, 2017. [See: US v Carpenter, 819 F.3d 880, 887 (6th Cir 2016)]

On August 7, 2017, Carpenter’s attorneys, many with the American Civil Liberties Union, filed the Brief for Petitioner. The brief presents an opportunity to highlight two things (a) the nature of the privacy interest at stake and (b) the mosaic theory of the Fourth Amendment.

(a) Privacy

The brief contains a considerable amount of information about smartphone privacy and the broad ramifications of stored digital data that I will edit as follows:

  • The density of cell sites continues to increase as data usage from smartphones grows. Because each cell site carries a fixed volume of data required for text messages, emails, web browsing, streaming video, and other uses, as smartphone data usage increases, carriers erect additional cell sites, each covering smaller geographic areas. This means that in urban and dense suburban areas like Detroit, many sectors cover small geographic areas. (pp. 3-4)
  • Service providers have long retained location information for the start and end of incoming and outgoing calls. Today, those companies increasingly also retain location information related to the transmission of text messages and routine internet connections – which smartphones make virtually constantly to check for new emails, social media messages, weather updates, and other functions. The information recorded can include not only cell site and sector, but also estimated distance of the phone from the nearest cell site. Location precision is also increasing as service providers deploy millions of “small cells,” “which cover a very specific area, such as one floor of a building, the waiting room of an office, or a single home.” All told, a typical smartphone connects to cell towers hundreds of times a day, generating a densely pixelated matrix of data points documenting the user’s movements. The volume and precision of that data will grow steadily in coming years, generating ever more granular locational information. (pp. 4-5)
  • The detailed and pervasive location records obtained in this case are far more comprehensive and sensitive than discrete telephone or banking information. And location data is not “voluntarily” conveyed by a phone user in the same sense as the information in Smith and [United States v Miller, 425 US 435 (1976)]. Cell phones are indispensable to participation in modern society – often required for employment, relied on for personal safety, and increasingly becoming essential medical treatment tools. Even if it could be said that possessing a cell phone is a voluntary act, it certainly cannot be said that cell phone owners knowingly and intentionally disclose their minute-by-minute movements in historical perpetuity. Carrying a smartphone, checking for new emails from one’s boss, updating the weather forecast, and downloading directions ought not license total surveillance of a person’s entire life. (p. 12)
  • As this Court’s decisions in US v Jones, 565 US 400 (2012) and Riley v California, 134 S Ct 2473 (2014), illustrate, the innovations of the digital age preclude wooden extension of analog-era precedents where technology has greatly increased the government’s ability to obtain intimate information. Extending Smith to CSLI would lead to unacceptable consequences. It would mean not only that CSLI is exempt from the Fourth Amendment, but also that persons would lack any reasonable expectation of privacy in the contents of emails and other communications that are necessarily shared with service providers to enable their transmission. People reasonably expect that the details of where they travel over an extended period are known only to themselves, and therefore cannot be obtained by the government without implicating the Fourth Amendment. (p. 13)
  • To be sure, the CSLI at issue here involves historical location data, rather than the real time tracking that GPS devices provide. But this only strengthens the claim for Fourth Amendment protection. Absent constitutional oversight, the availability of CSLI records would make it “relatively easy and cheap” for the government to pervasively track virtually any American. (p. 19)

Most smartphones, such as Apple’s iPhone, have a location privacy setting that, when activated, prevents applications such as a GPS app from accessing the phone’s location. But this function does not shield the phone from the service provider’s ability to log and retain the phone’s cell tower location. As the brief asserts, at p. 42: “Virtually any use of the phone generates a location record. There is no option to close the proverbial phone booth door.”

(b) Mosaic Theory

In US v Jones, 132 S Ct 945 (2012), where GPS surveillance was in issue, five justices joined in a new approach to interpreting Fourth Amendment protection. Prior to Jones, Fourth Amendment decisions evaluated each step of a police investigation individually. But the opinions in Jones introduced what has been called a “mosaic theory” of the Fourth Amendment by which a collective sequence of government activity is evaluated as an aggregated whole in order to consider whether the sequence amounts to a search. The brief makes these submissions about the unprecedented surveillance time machine that CSLI provides:

  • When the government employs new technology to obtain sensitive personal information in a way that diminishes the degree of privacy that individuals reasonably expected prior to the technology’s adoption, it conducts a search under the Fourth Amendment. (p. 10)
  • For the same reason that five Justices [in Jones] concluded that there is a reasonable expectation of privacy in longer-term GPS monitoring of a car, there is a reasonable expectation of privacy in longer-term cell phone location records. Any other conclusion would allow the government to circumvent the principle accepted by five Justices in Jones through the simple expedient of obtaining cell phone location records. People use their cell phones throughout the day – when they are at home, work, or school, when they are in the car or on public transportation, when they are shopping or eating, and when they are visiting the doctor, a lawyer, a political associate, or a friend. People often keep their phones nearby and turned on while they are asleep. Indeed, “nearly three-quarters of smart phone users report being within five feet of their phones most of the time, with 12% admitting that they even use their phones in the shower.” Riley, 134 S Ct at 2490. (pp. 16-7)
  • “[D]etails about the location of a cell phone can provide an intimate picture of one’s daily life.” State v Earls, 70 A.3d 630, 642 (NJ 2013). Historical CSLI “can reveal not just where people go – which doctors, religious services, and stores they visit – but also the people and groups they choose to affiliate with and when they actually do so.” Commonwealth v Augustine, 4 NE 3d 846, 861 (Mass 2014) (quoting Earls, 70 A.3d at 642). And to state the obvious, when people make a “visit to a gynaecologist, a psychiatrist, a bookie, or a priest,” they typically “assume that the visit is private.” United States v Davis, 754 F.3d 1205, 1216 (11th Cir 2014) (Sentelle, J.), rev’d en banc, 785 F.3d 498 (11th Cir 2015). (p. 17)

In an article titled ACLU: Absent warrant standard, police could monitor anyone via location data published by Ars Technica on August 9, 2017, Cyrus Farivar put it this way: “Justice Sotomayor [in Jones] alluded to what is often referred to in academic circles as the ‘mosaic theory,’ the notion that the sum total of data gathered is often more revelatory than the discrete data collected. As such, some privacy activists argue, potentially revelatory data – like CSLI – should require a warrant.” Some discussion on social media, such as Twitter, quoted by Mr. Farivar, was critical of the Carpenter brief for advancing an argument on the basis of the mosaic theory. The theory has been criticized for being unworkable in practice. There is no bright line. [See: Orin Kerr. The Mosaic Theory of the Fourth Amendment, 111 Mich L Rev 311 (2012)]


As smartphones become more embedded in our daily lives, the Carpenter brief is a good example of what should be obvious. Digital data stored by service providers is not just another third party record. As Tim Cushing said in a piece titled ACLU Tells Court Long-Term Cell Site Location Tracking Should Require A Warrant published by TechDirt on August 11, 2017, cell site location data is a “proxy tracking system for law enforcement” where almost every citizen carries a “government tracking device wherever they go.”

Comments are closed.