Cell phones are a ubiquitous part of our modern life. It’s easy to forget that they are constantly tapping into the wireless networks around us several times a minute, even when we’re not using them. Each time a cell phone connects to a cell tower or cell site, it generates a time-stamped record known as Cell-Site Location Information (CSLI). Wireless carriers collect and store their customer’s increasingly precise CSLI generated from incoming calls, text messages, and routine data connections. Would you expect these CSLI records maintained by your service provider to remain private? What if the police wanted access to them as part of an investigation of a crime? Should they be expected to obtain a warrant in order to obtain them?

The recent U.S. Supreme Court case of Carpenter v. United States dealt with that very issue. In a 5-4 ruling, the Court held that “an individual maintains a legitimate expectation of privacy in the record of his physical movements as captured through CSLI.” Accordingly, the Court ruled that the government generally needs a warrant to collect customer’s location dates from cellphone companies. In so doing, the Court recognized that “[i]n light of the deeply revealing nature of CSLI, its depth, breadth, and comprehensive reach, and the inescapable and automatic nature of its collection, the fact that such information is gathered by a third party does not make it any less deserving of Fourth Amendment protection.”

While this case was narrowly focused on historical CSLI data and the Fourth Amendment rights of a criminal defendant, and recognized that warrantless searches related to bomb threats, active shootings, and child abductions may still be approved, it nonetheless represents an important recognition by the Court of the interconnected, digital reality in which we now live. While the Court was careful to state that its decision is not intended to address anything other than the historical CSLI data at issue, other courts and litigants may seek to expand the Court’s reasoning and holding to other forms of cellphone and email data.