Timothy Carpenter was convicted of a string of robberies partly on the basis of 127 days of cell-site location records the government obtained from his carriers under the Stored Communications Act's lower court-order standard. Chief Justice Roberts's opinion narrowed the third-party doctrine (Smith v. Maryland, United States v. Miller) as applied to digital-era data: because cell-site records reveal 'an intimate window' into a person's movements and are collected passively, without any meaningful voluntary disclosure, they receive Fourth Amendment protection. Law enforcement generally needs a probable-cause warrant. Carpenter is the most important Fourth Amendment decision of the digital age and the analytical starting point for every subsequent case on cloud data, geolocation, and network surveillance.