Even after January's landmark Supreme Court decision cast significant doubt on the government’s ability to electronically track a person’s location without a warrant, the Justice Department continues to defend this practice. On Friday, the ACLU, along with the Electronic Frontier Foundation, the Center for Democracy and Technology, and the National Association of Criminal Defense Lawyers, filed a friend-of-the-court brief in the U.S. Court of Appeals for the Fifth Circuit, arguing that the government should be required to obtain a warrant based on probable cause before seizing 60 days’ worth of location information generated by an individual’s cell phone.

The appeal by the government comes after a federal district court judge in Texas held that the constitution does indeed require a warrant for such information. As long as a cell phone is turned on, it automatically registers its estimated location with the nearest cell towers as frequently as every seven seconds. This means that every person who uses a cell phone is creating a vast record of personal information, from doctors’ visits to church attendance to visits to friends’ homes.

In our brief, we urge the court to hold that the Fourth Amendment requires the government to obtain a warrant and demonstrate probable cause before obtaining cell phone location data. Most people are unaware that their every movement can be tracked through their phones, and we maintain an expectation that such information will remain private. Cell phone location data, especially data collected over a prolonged period of time, is simply too sensitive to allow the government access without proving to a judge that there’s good reason to believe it will turn up evidence of a crime.

This is the first time in years that a higher court will consider the constitutionality of this issue. By refusing to appeal lower-court decisions where a judge required a warrant, the government has avoided allowing appeals courts to make a ruling.

Unfortunately, the government believes that most people know that their cell phones are generating a near-constant record of their locations and movements, and it argues that individuals cannot reasonably expect that this information will remain private.

The government is wrong. We shouldn’t have to choose between using the modern technology that society has come to rely upon and being able to expect that our private information will remain private. Instead, our brief encourages the court to recognize that when we take our cell phone to the gym or to a political rally, we certainly don’t intend for the government to be following along.

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