THE CURIOUS CASE OF CELL PHONE LOCATION DATA: FOURTH AMENDMENT DOCTRINE MASH-UP

INTRODUCTIONThe third-party and public disclosure doctrines are longstanding hurdles to Fourth Amendment protection. Federal courts have recently invoked these doctrines to determine whether police can acquire cell phone location data from providers without constitutional scrutiny.1 These rulings are all over the map. Courts disagree not only on whether location information is constitutionally protected but also if one, both, or neither of these doctrines applies. The Supreme Court has yet to enter the fray. So for now, we are left with muddled results.2 A major reason for the confusion turns out to rest on a hitherto overlooked tension between the two doctrines. This Essay is the first to raise this issue and, in turn, harmonize these doctrines in the cell phone location data context.3While both doctrines vitiate privacy protection and are often associated together, they rest on unique foundational triggers.4 The thirdparty doctrine involves an individual voluntarily disclosing nonpublic information to an actual person or entity. The Supreme Court has applied this doctrine to statements made to undercover informants,5 bank records released to banks,6 and telephone numbers disclosed to phone providers.7 The public disclosure doctrine, on the other hand, focuses on a suspect making voluntary public movements that are susceptible to visual surveillance. The Court has applied this doctrine to police surveillance of suspects using beeper technology8 or a GPS device.9Courts seem to pick and choose a doctrine when analyzing cell phone location data, with little to no analysis on why one or the other applies (or doesn't apply).10 These inconsistent choices are primarily due to the unique nature of this technology and the different ways one can conceptualize how the government collects it. The data can be viewed as nonpublic information disclosed to a cell phone provider, suggesting a potential application of the third-party doctrine, or as public movements susceptible to visual surveillance, suggesting a potential application of the public disclosure doctrine. But the key to applying the right doctrine is recognizing in which of these two contexts the government activity is taking place. It matters, for example, whether the government is seeking historical cell phone location data or acquiring real-time data. This Essay provides the first workable topology for these various scenarios and, in the process, offers some much overdue clarification on the operative elements of the respective doctrines.Part I introduces how cell phone location data is created and collected. Part II details the contours of the third-party and public disclosure doctrines. Part III highlights the split among federal courts regarding whether the Fourth Amendment protects against the collection of cell phone location data, particularly in light of the varying applications of the third-party and public disclosure doctrines. Part IV outlines an approach for determining which of the two doctrines should apply. Finally, the Essay concludes by noting the implications of the cell phone location data Fourth Amendment conundrum for future technological developments.I. A PRIMER ON CELL PHONE LOCATION DATACell phones use radio waves to connect to their service providers to facilitate a host of functions, including making and receiving phone calls, sending and receiving text messages, and using the Internet.11 Cell phone providers, in turn, maintain thousands of cell phone towers that receive these radio signals.12 Cell phones emit these signals anytime they are turned on, after which the nearest cell phone tower acquires a signal.13 This process is automatic, without any notice to the user, and a user does nothing to facilitate the transmission except turning on the phone.14 The signal moves from tower to tower as a cell phone user changes location and the location of the nearest tower is transmitted to the provider.15 Cell phone company privacy policies typically include language that a user's location is collected in the foregoing way. …