AMY PEIKOFF: The Supreme Court’s Opportunity to Legalize Privacy.

Enduring, reliable protection for the data we share with third parties must come from the Fourth Amendment. This is precisely the opportunity presented by Carpenter v. United States, soon to be heard by The Supreme Court.

Carpenter concerns the application of the third-party doctrine to Cell Site Location Information (CSLI) collected by service providers. Petitioner Carpenter argues that, unlike other data shared with a third party, longer-term cell phone location data (here collected for 127 days) is something in which one has a “reasonable expectation of privacy.” (“Reasonable expectation of privacy” is the standard the Court uses to determine whether a search has occurred within the meaning of the Fourth Amendment.) Accordingly, Carpenter argues that the third-party doctrine should apply neither to longer-term cell phone location data, nor to similarly sensitive data: “There is no basis in [the Supreme] Court’s jurisprudence for extending Smith and Miller [cases extending the third-party doctrine to ‘ordinary business records’] to CSLI, both because the information is more sensitive, and because it is not voluntarily shared with a third party in any meaningful way.”

Once you extend the scope of the third-party doctrine to “ordinary business records,” how do you draw even a semi-bright line, particularly one for which there is a principled rationale? How long is the “long-term” over which one’s data is collected, before one’s expectation of privacy becomes “reasonable”? Why shouldn’t digital information be subsumed if analog is? How sensitive is sensitive? And so on.

The Court should overturn Smith and Miller, and return the third-party doctrine to its original scope: sharing information with government agents in the course of criminal activity.

Read the whole thing.