Brief of Scholars of the History and Original Meaning of the Fourth Amendment as Amici Curiae in Support of Petitioner in Carpenter v. United States

Privacy and Security

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Danielle Citron, Morgan Cloud, William J. Cuddihy, Laura Donohue, Norman Garland, David C. Gray, Margaret Hu, Renee M. Hutchins, Tracey Maclin, Luke Milligan and George C. Thomas


Southwestern Law School Research Paper No. 2017-10, August 2017


Police use data from cell phone providers to track the movements of suspects over a long period of time. Unlimited access to such data threatens privacy rights protected by the Fourth Amendment.

Policy Relevance

Courts should require police to obtain a warrant to access tracking data from cell phone companies.

Main Points

  • In the case of Carpenter v. United States, law enforcement officials used records from a robbery suspect's cellular phone service provider to show the suspect's whereabouts over a four month period.
  • In the eighteenth century, when the Fourth Amendment was ratified, the word "search" meant to examine, explore, or try to find; police use of cell phone records was a "search" that implicates Fourth Amendment privacy rights.
  • Fourth Amendment privacy rights were intended to prevent the government from conducting searches using anything that resembled British “general warrants,” which gave authorities broad discretion to search wherever they pleased.
  • In the eighteenth century, jurists who opposed the general warrant explained that their concerns were not confined to situations in which authorities did not physically intrude upon a home or papers, but also included concerns about access to information or prying.
  • The drafters of the Fourth Amendment did not anticipate cell phone technology, but would have rejected the state's claim that it had unlimited authority to conduct a search for evidence of criminal activity.
  • Cell site location data could potentially reveal insight into intimate relationships and religious and political activities over a long period of time, just like a general warrant.
  • The Stored Communications Act (SCA) limits government access to cell site location information, but was passed before telephone records allowed the police to track subscribers' movements.
    • SCA safeguards are insufficient, because the law does not require the police to show probable cause to suppose that the cell site location data will produce evidence of the crime under investigation.
    • The SCA does not limit the breadth of searches that use cell site location information.

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