By Connor Finch, Legal Fellow

If you are near your cell phone and your phone is on, your wireless provider – not to mention the developer of any app on your phone – knows where you are. And given its economic value, companies routinely store all location data. Should the government be required to get a warrant to have wireless companies provide information about everywhere you have been in the previous days, weeks, months, or years?

In 2011, the Detroit police department arrested Timothy Carpenter and three others thought to have robbed eight retail stores. In order to strengthen the criminal case, federal prosecutors wanted Carpenter’s wireless provider, MetroPCS, to provide all location data on Mr. Carpenter for a four-month period. Rather than getting a warrant, which requires the police to have probable cause, the federal government relied on a federal statute with a much lower standard. Under that law, the prosecutor only had to show that the police had “reasonable grounds to believe” that the records “are relevant and material to an ongoing criminal investigation.” MetroPCS ended up handing over 186 pages of cell phone location records covering movements Carpenter made over four months.

When Mr. Carpenter challenged the warrantless search, The ACLU, along with the ACLU of Michigan, Brennan Center, Center for Democracy & Technology, Electronic Frontier Foundation, and National Association of Criminal Defense Lawyers, filed an amicus brief arguing that the government violated the Fourth Amendment when it obtained the location records from Mr. Carpenter’s wireless carrier without a warrant. A lower federal court has said the government did nothing wrong. Relying upon the antiquated “third-party doctrine,” the court ruled that because Carpenter willingly handed over the information to the phone company, his location data is not private information protected by the Fourth Amendment. But, as the Supreme Court recognized in 2014, cell phones have fundamentally changed society, and Fourth Amendment jurisprudence must adapt.

No one should have to trade away their Fourth Amendment rights to use a smartphone. Therefore, the ACLU joined Mr. Carpenter’s defense attorney as co-counsel and appealed to the Supreme Court. After today’s oral argument, the Supreme Court will decide whether people’s locations can be tracked without a warrant. If the Supreme Court upholds the lower court’s antiquated reasoning, suspected criminals like Mr. Carpenter are not the only people at risk. Without needing a warrant, it would be easier for the government to track anyone they think might have evidence of illegal activity. It would also be easier to track the movements of investigative journalists and advocates for undocumented people.

In short, private companies now hold more information on Americans than any historical police state could have possibly acquired. In order to preserve our liberties, the Supreme Court should protect location information with the tried and true warrant requirement. Otherwise, it is up to Congress.