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Are the police allowed to use a time machine to investigate you?

Imagine if the government possessed a device which could, with the push of a button, display a citizen’s every movement for the prior year with pinpoint accuracy.  The device could reveal its target’s trips to medical appointments, political meetings, private residences, and even into and out of the shower with exact time frames and locations.  Now, further imagine that the government could use this device to monitor the past of anyone - without a warrant or evidence of a crime.

 This “time machine” exists and is described in the United States Supreme Court case of Carpenter v. United States.  The device at issue is not the time machine of science fiction, but rather a type of data known as cell-site location information (“CSLI”), which runs constantly on all cell phones.  CSLI pinpoints the location of a cell phone over one hundred times per day and reports that information to the cell carrier, which, until the Carpenter case, had been free to pass it along to the police without a warrant.  It amounted to, as the Supreme Court noted, “Twenty-four hour surveillance of any citizen of this country.”  “Accordingly, when the Government tracks the location of a cell phone it achieves near perfect surveillance…with access to CSLI, the Government can now travel back in time to retrace a person’s whereabouts.”  The investigators in Carpenter had minimal information about the accused until they used the procedure, which then gave them over one hundred data points per day about his whereabouts over 127 days.  The fact that the police acted without a warrant went too far, the court held, stating:  “an individual maintains a legitimate expectation of privacy in the record of his physical movements as captured through CSLI.”  Thus, from now on, police must have a warrant to obtain this type of information.  The government is now forbidden from undertaking general surveillance of the past.

Imagine the implications of the government gaining access to one’s complete electronic footprint without a warrant.  Today, many people log their body’s vital signs into a fitbit, food they consume into a diet tracker, and let devices record almost every word they speak in their homes (yes, this happens).  Even more than in 2018, when the Carpenter case was decided, technology provides an almost perfect window into your past.  The Fourth Amendment, more influenced by technology than any other, will continue to be tested as these digital windows into the past become clearer.