One of the most important Fourth Amendment cases in years is being considered by the Supreme Court during its October 2017 term. The case, Carpenter v. United States, concerns whether historical cell site location information (“CSLI”) should be protected under the Fourth Amendment, requiring law enforcement to first obtain a search warrant before requiring wireless service providers to hand over CSLI related to a subscriber.

The Court’s decision is sure to affect surveillance laws, but it also could shape how the Fourth Amendment applies to modern technology. Most Americans carry a smartphone with them at all times. A wide variety of Internet-connected devices are now found in many homes. Connected cars have become standard. All of these devices collect information about how, when, and where they are used – data that is very similar to the CSLI at issue in Carpenter.

Up to now, courts have generally classified CSLI as business records not entitled to Fourth Amendment protection. Law enforcement may acquire CSLI using an “articulable facts” court order in accordance with the processes set out in the Stored Communications Act. Whether CSLI are business records that fall within the third-party doctrine has been fiercely debated by legal scholars, privacy experts, lawmakers, and federal and state courts of all levels.

Carpenter v. United States comes to the Supreme Court from the U.S. Court of Appeals for the Sixth Circuit. In the case below, a divided three judge panel concluded that CSLI are business records used by wireless service providers to connect and maintain calls. The majority opinion distinguished the content of communications from CSLI, explaining that “[c]ontent...is protected under the Fourth Amendment, but routing information is not.” [1] The majority held that the government’s collection of historical CSLI was not a search under the Fourth Amendment.

The majority opinion likened historical CSLI to plain old telephone service calling records that the Supreme Court held in 1979 were not entitled to Fourth Amendment protection. Yes, you read that right. The Sixth Circuit said CSLI are similar to landline telephone calling records.

In one respect, the numbers someone dials to make a landline phone call are similar to CSLI – both are used by third-party service providers to facilitate communications between people. But, that is where the similarity ends. The data produced by CSLI is enormous. CSLI provides a detailed picture of the whereabouts, actions, and personal life of an individual. Records of telephone numbers someone dials provide only a glimpse of such information. CSLI data reveal a scope of information far beyond that of landline telephone business records.

The paragraphs below argue that for purposes of the Fourth Amendment, courts should not categorize historical CSLI as business records. They first summarize the creation of the Supreme Court’s third-party doctrine in Smith v. Maryland, and then compare two types of business records – telephone numbers recorded from a pen register and precise CSLI data produced by modern smartphones.

The “third party doctrine” provides that there is no Fourth Amendment protection for information a person voluntarily discloses to a third party. 

The Supreme Court developed the third party doctrine over the course of about 25 years in cases concerning undercover agents and informants [2] and opinions related to business records. [3] Two particular cases from the 1970’s articulate the application of the third party doctrine – United States v. Miller, involving banking records, and Smith v. Maryland concerning the use of a pen register.

The facts of Smith v. Maryland correspond to Fourth Amendment concerns that are raised by the use of the Internet and advanced communications services, making the Court’s reasoning in Smith useful for analyzing Carpenter. In Smith, a telephone company installed a pen register at the company’s central office at the request of law enforcement to record the numbers dialed from Michael Lee Smith’s home phone. The police did not have a warrant. Information produced by the pen register showed that Smith called the home phone of a woman that Smith was suspected robbing.  Based on this information and other evidence, law enforcement secured a search warrant for Smith’s house, and following a search, arrested him.

At trial, Smith moved to suppress all evidence derived from the pen register, arguing law enforcement should have obtained a warrant before having it installed. The trial court denied the motion and convicted Smith. The Maryland Court of Appeals affirmed, holding Smith had no expectation of privacy in the phone numbers he dialed.

Applying the legitimate expectation of privacy standard established in Katz v. United States, [4] the Supreme Court rejected Smith’s claim that he had a reasonable expectation of privacy in his telephone metadata, concluding that unlike the contents of communications, there is no legitimate expectation of privacy in the numbers that one dials when using the telephone. The Court explained that people are aware that the telephone company collects this information to determine a subscriber’s monthly bill, to detect fraudulent calls, to prevent harassing calls, and for other legitimate business purposes. The Court then reaffirmed its prior holding in United States v. Miller, and provided a more succinct explanation of the third-party doctrine: “a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties.” [5]   In the context of using communications services, once an individual places a call or sends a message, he discloses certain information needed by the third party service provider to make it happen. At the same time, he loses Fourth Amendment protection of that information, regardless of what he may expect.

In Smith v. Maryland, police installed a pen register to see whether a single person would call a single telephone number. 

The events in Smith transpired during a time when plain old telephone service was the primary form of communications, and the Supreme Court’s subjective view of society’s expectations of privacy when using that service is based on the characteristics that technology. Since Smith, communications technology has astonishing advancements – from wireline to wireless, and analog to digital.

Today, smartphones and other wireless devices keep people in constant contact everywhere they go and at any time. Smartphones allow people to receive a work call or email when away from the office, place a call to public safety after an accident, or check the score of a baseball game using an app they downloaded.

Collection of CSLI is distinctly different from the way phone records were collected in Smith. There, the pen register recorded information conveyed by a person actively dialing phone numbers, and that information was of limited scope and sensitivity.

Today, unbeknownst to most users, modern cell phones constantly ping network cell towers in search of the nearest or strongest base station. Why? A wireless network needs to know the location of a cell phone in order to send and receive voice and data communications to and from the device. When a cell phone communicates with a cell tower, a CSLI record is generated. CSLI typically identifies the tower used, the time and date, the direction of the wireless signal from the cell tower which indicates the cell sector, along with other data concerning the interaction between the cell phone and tower. A single wireless phone can produce over one hundred SCLI data points per day. [6] These CSLI records can be used to “reconstruct someone’s specific movements down to the minute,” [7] a tool much more powerful than what can be done with records produced by a pen register.

Two key aspects of CSLI produced by wireless smartphones should play an important role in the Supreme Court’s review of Carpenter. First, smartphones passively produce massive amounts CSLI data, and second, that data can be very revealing. One more thing is important to note – the CSLI at issue in Carpenter was produced in 2010 and 2011. The wireless industry has moved to LTE since then, and wireless networks have added thousands of new cell sites. The precision of CSLI has improved, and will only get better.

So there you have it. CSLI records are very different from records produced by a pen register. This leads to the next question – do the characteristics of CSLI change the reasonable expectation of privacy analysis? Yes, over half of the Supreme Court’s Justices told us that in U.S. v. Jones.

[1] U.S. v. Carpenter, 819 F.3d 880, 883-884 (6th Cir. 2016).

[2] See e.g., On Lee v. United States, 343 U.S. 747 (1952); Lopez v. United States, 373 U.S. 427 (1963); United States v. White, 401 U.S. 745 (1971).

[3] See e.g., Couch v. United States, 409 U.S. 322 (1973); United States v. Miller, 425 U.S. 435 (1976); Smith v. Maryland, 442 U.S. 735 (1979).

[4] 389 U.S. 347 (1967).

[5] Smith v. Maryland at 743-744 (citing Unites States v. Miller at 442-444).

[6] U.S. v. Graham, 796 F.3d 332, 350 (4th Cir. 2015).

[7] Riley v. California, 134 S. Ct. 2473, 2490 (2014) (citing U.S. v. Jones, 565 U.S. 400, 415 (2012) (Sotomayor, J., concurring)).