Abstract: In 2012, federal juries convicted two men of armed robbery based in part on historical cell site location information (“CSLI”) evidence. Historical CSLI can reproduce a person’s location with great specificity. Cell phone users generate CSLI automatically by operating their cellular phones. These facts raise serious privacy concerns. This Note argues that Congress must take action to ensure that law enforcement agents can access a suspect’s historical CSLI only after a neutral magistrate finds probable cause that a crime has been committed. Further, this Note argues that because cell phone users do not voluntarily convey CSLI to their phone companies, the government may not, absent a probable cause warrant, access that information by invoking the third party doctrine announced by the U.S. Supreme Court in its1979 decision in Smith v. Maryland.