California Forum

The government can track you on your cellphone. Doesn’t that invade digital privacy?

Smart phone technology records a user’s whereabouts every time a cell tower picks up a signal. Carpenter v. United States, pending before the U.S. Supreme Court, asks whether existing law should be updated to require a court warrant for such data before it is released to third parties, such as the government or police.
Smart phone technology records a user’s whereabouts every time a cell tower picks up a signal. Carpenter v. United States, pending before the U.S. Supreme Court, asks whether existing law should be updated to require a court warrant for such data before it is released to third parties, such as the government or police. AP

A case argued a few weeks ago in the United States Supreme Court provides a crucial vehicle to bring the law of privacy into the 21st century.

Timothy Carpenter was suspected of committing a series of armed robberies. The FBI went to his cellphone company and got the cell tower records that revealed his location and his movements for 127 days. The FBI received this information without a warrant from a judge. The cell tower information was crucial evidence used to convict him and sentence him to 119 years in prison.

Every time we use our cellphone – to send and receive calls or texts or emails or access the internet – it connects to cell towers. The records – generated hundreds and sometimes thousands of times per day – include the precise GPS coordinates of each tower as well as the day and time the phone tried to connect to it. It is possible to determine our location at almost any point in time and track our movements through this information. The police constantly use this technology. In 2016, Verizon and AT&T alone received about 125,000 requests for the cellular information from law enforcement agencies.

A great deal can be learned about a person from this information. As one court explained, ‘[a] person who knows all of another’s travels can deduce whether he is a weekly church goer, a heavy drinker, a regular at the gym, an unfaithful husband, an outpatient receiving medical treatment, an associate of particular individuals or political groups – and not just one such fact about a person, but all such facts.’

The issue in Carpenter v. United States is whether the Fourth Amendment, which prohibits unreasonable searches and arrests, requires that the police obtain a warrant in order to access this information. The Fourth Amendment, and its warrant requirement, is an essential protection of our privacy. It demands that the police show a judge that there is probable cause – good reason to believe that evidence of a crime will be obtained – before there is a search.

It is frightening to realize that the government can track virtually all of us and our movements any time it wants just by asking for our cellphone records. A great deal can be learned about a person from this information. As one court explained, “[a] person who knows all of another’s travels can deduce whether he is a weekly church goer, a heavy drinker, a regular at the gym, an unfaithful husband, an outpatient receiving medical treatment, an associate of particular individuals or political groups – and not just one such fact about a person, but all such facts.”

From the oral argument held on Nov. 29, it is apparent that the justices are divided. The court last dealt with a similar issue in 2012 in United States v. Jones. The police put a GPS device on the undercarriage of Antoine Jones’ car without a valid warrant and tracked his movements for 28 days. The court unanimously held that this violated the Fourth Amendment. Justice Antonin Scalia wrote the opinion for the court and held that putting the GPS device on the car was a trespass.

He relied on an English law precedent from 1765. But what if the police had tracked Jones’ movements, not through a GPS device physically placed on the car, but rather through cellular or satellite technology? That is precisely the issue in Carpenter v. United States.

Every federal court of appeals to consider the issue has held that no warrant is required before police access cellular location information. These courts have relied on a legal principle called the “third party doctrine” – that we have no privacy interest in information that we share with a third party, such as a phone company.

For example, in Smith v. Maryland in 1978, the court held that police do not need a warrant to obtain from the phone company a record of the numbers that we dial or receive calls from because we should not be able to expect that the third party, the phone company, will keep the information secret. The court has applied this to say that the police can obtain our banking information, such as records of our deposits and withdrawals, without a warrant because a third party (the bank) has the information.

As Justice Sonia Sotomayor pointed out in her separate opinion in United States v. Jones, the third-party doctrine “is ill suited to the digital age.” She explained that we live in an era “in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks.” The ability of the police to track our movements through technology is constantly expanding.

The court in Carpenter should hold that the government should be able to obtain this information only by getting a warrant from a judge based on probable cause. This will not preclude police from obtaining the information where they have a valid basis, but it will provide all of us with the essential protection of privacy that the Fourth Amendment demands.

Erwin Chemerinsky is dean and professor of law at the UC Berkeley School of Law. He can be reached at echemerinsky@law.berkeley.edu.

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