Cellular Privacy: Supreme Court Rules to Protect Historical Cellphone Location Data


By: Ariana Morello

On June 22, 2018 in Carpenter v. United States the United States Supreme Court held that police must have a warrant and show probable cause when retaining cell-site location information (CSLI), which is the information nearby towers gather from cell phones.  In a close 5-4 decision, the Court found that a cell phone user has a legitimate expectation of privacy and CSLI data obtained from a cell phone carrier company qualified as a “search” under the Fourth Amendment.

Background of the Case 

In this influential case, the Supreme Court addressed whether retaining a person’s historical cell-site information without probable cause violated the Fourth Amendment, which protects people from unreasonable searches and seizures of property.  The defendant, Timothy Carpenter, was identified as one of several suspects in a series of robberies that took place in 2011. The prosecution was granted a court order under the Stored Communications Act (SCA) to obtain Carpenter’s CSLI records from MetroPCS and Sprint.  The SCA only requires the government show “reasonable grounds” for believing records are relevant to an ongoing investigation, which includes a reasonable belief a crime has been committed. They need not show the higher standard of probable cause, which involves more concrete evidence, to obtain CSLI.

The order for Carpenter’s CSLI disclosed 152 days of CSLI from MetroPCS and seven days of CSLI from Sprint.  In total, the government obtained 12,898 location points that proved Carpenter was “right where the . . . robbery was at the exact time of the robbery.”  Carpenter was found guilty and sentenced to more than 100 years in prison.

What is CSLI?

CSLI is the information a wireless carrier collects as a cell phone gives its location to nearby cell towers, called cell sites.  Since wireless carriers need to reach individuals when they receive a call, CSLI is constantly being created whether or not the individual is using their phone. Any activity generates CSLI, including texts, emails, or applications.

Cell-site towers contain multiple antennae that detect signals from phones and connect phones to a network.  As they move further from one site and closer to the next, phones automatically transfer the connection to a new tower.  Though cell sites are normally located on towers, they have also been mounted on “light posts, flagpoles, church steeples, or the sides of buildings”-they are everywhere.  Through a process called triangulation, multiple towers are used to pinpoint a signal.  By measuring signal strength and the time it takes to receive a signal back, a tower can determine a cell phone’s distance from the cell-site.  Urban areas, which have more towers than rural areas, produce more accurate location information.

It is estimated that there are over 701,000 cell-sites in the U.S., including over 1.97 million antennae.  To put things in perspective, within a one-mile radius of downtown Seattle, there are an estimated 125 towers and 815 antennas tracking your location.

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CSLI Demands by Police are Increasing

Cell companies store both historical and prospective CSLI.  Historical CSLI tracks past movements of a cell phone, whereas prospective CSLI can be used in real time to track a person’s movements as they occur.  This information is stored by service providers for years.

Police use CSLI to place a suspect a the scene of a crime and provide evidence that will lead to a suspect’s conviction.  Not only can police place suspects within 50 meters of a location, but small base stations designed for individuals in a home or building can determine a phone’s location with GPS-like accuracy.

Based on Verizon’s transparency report, Verizon received 21,863 demands for CSLI during the first half of 2018.  Similarly, AT&T’s transparency report shows that from January to June 2018, AT&T received over 42,000 location demands which included historic and real-time CSLI.  This is an increase from the 37,670 requests received by AT&T from July to December 2017.  These demands “seek precise GPS coordinates of the device or call details records that reflect the locations of any cell site processing a call.”  According to AT&T, a single demand may cover multiple towers.

The Supreme Court Decision

The Court ruled that accessing CSLI constitutes a “search” under the Fourth Amendment; to allow the police to access such a plethora of information without a warrant would be unconstitutional.

The Fourth Amendment of the United States protects an individual’s right to privacy, prohibiting  “unreasonable searches and seizures” without a warrant and probable cause.  The Supreme Court declined to extend the “third-party doctrine” which states an individual has no expectation of privacy when information is disclosed to a third-party.  Thus, though data from cell phones is collected from cellular carriers, a cell phone user still has a reasonable expectation of privacy.

The Supreme Court explained, even if one is in an area accessible to the public, what one seeks to protect as private may be constitutionally protected.  In its reasoning, the Court pointed to the “exhaustive chronicle” of information collected by cellular carriers not just on a defendant, but on all citizens.  Since records are kept for years, “Unlike the nosy neighbor who keeps an eye on comings and goings, [service providers] are ever alert, and their memory is nearly infallible.”

The Supreme Court reasoned that because we are never far from them, cellphones have become a part of our anatomy.  CSLI can provide an “intimate window into a person’s life, revealing not only his particular movements, but… his ‘familial, political, professional, religious, and sexual association.’”  Thus, the Court advanced a policy argument favoring a higher standard of proof, preventing the police from prying at will into the CSLI of unsuspecting citizens.

Decision Limitations 

The Supreme Court maintained a narrow holding and refused to address any issues outside of historical CSLI.  Prospective CSLI as well as tower dumps, conventional surveillance techniques, and business records of location information were left untouched.

Further, the Court noted an exception to their holding allowing police to request CSLI without a warrant if “the exigencies of the situation” make it necessary.   These exigencies include pursuit of a suspect, protecting individuals in imminent harm, and preventing the destruction of evidence. Since the ruling only applies to historical CSLI, it is likely future issues will arise and the courts will have to address the legality of other types of CSLI.






















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