Law Enforcement Needs a Warrant to Obtain Cell-Site Location Data

July 02, 2018
University of Illinois College of Law's Jay Kesan

University of Illinois College of Law's Jay Kesan

University of Illinois College of Law

Cellular service providers store information about which cell towers transmit signals to a customer’s phone, thus revealing the geographic area where you are located when the transmission occurs.  When cell phones were first getting popular, this information would be limited to when a phone call or text message was initiated or received by an individual, and the information only provided a general vicinity of where the cell phone was located. 

Modern apps often give users the option to receive “push” notifications that allow services to send updates directly to your phone instead of waiting for you to manually check for updates.  The frequent “checking in” from apps makes cell site location data increasingly detailed, and service providers might store this information for years. Because people carry their phones with them, historical cell site location data creates the new possibility of retroactive surveillance as a boon to law enforcement.   

On June 22, the Supreme Court issued its opinion in the case of Carpenter v. United States. Carpenter concerned this type of cell site location information and involved a string of robberies in Michigan and Ohio. The defendant’s physical nearness to the robberies, as shown by historical cell site data, was used as circumstantial evidence to support convicting him. To obtain this information, the investigators had used an order under the Stored Communications Act.

This order is an enhanced subpoena process to allow investigators to compel certain categories of data from cellular service providers without having to show the full “probable cause” that is required for a warrant under the Fourth Amendment.

In Timothy Carpenter’s case, investigators used this enhanced subpoena to obtain 127 days of information about Carpenter’s physical movements, consisting of 12,898 individual data points. The question before the Supreme Court was whether investigators needed to show “probable cause” to obtain a court order to conduct this kind of retroactive surveillance.

A 5-4 majority on the Supreme Court noted that the Carpenter case exists at a crossroad in Fourth Amendment law. On one hand, in the recent GPS-related case of United States v. Jones, the Supreme Court recognized an expectation of privacy in physical location and movements. But there is also the third-party doctrine, which says there is not an expectation of privacy in information that you voluntarily give to third parties.  The third party doctrine is often discussed in the context of business records, like financial records held by a bank.

In the Carpenter decision, the Supreme Court ruled that the third party doctrine does not apply to historical cell site location data. The Court reasoned that even in third party doctrine cases, Fourth Amendment protection may still exist for information of a particular nature. Writing for the majority, Chief Justice Roberts noted that “[t]here is a world of difference between the limited types of personal information addressed in [third party doctrine cases] and the exhaustive chronicle of location information casually collected by wireless carriers today.”  

The Carpenter decision, while potentially ground breaking for privacy rights, is fairly narrow and is very much tied to the presence of physical objects.  Under Carpenter, there is Fourth Amendment protection for this kind of automatically generated information that tracks locations for a particular communications device. Previous cases about location privacy under the Fourth Amendment have concerned beepers in barrels and GPS devices in cars.  Cell site data is more far-reaching because cell phones are practically an extension of the body.

This action by the Supreme Court recognizes the societal developments that come with living in a highly connected technological age. If you want a device to be able to connect to services wirelessly, some form of location tracking will occur. Carpenter clarifies that that kind of information is to be afforded Fourth Amendment protections.