All too often, new police surveillance tools are initially applied to only the “worst of the worst” and then slowly—but surely—expanded to include an ever-growing number of less culpable individuals. We’ve seen it with DNA collection. And now we’re starting to see it with GPS tracking. That’s why last week EFF filed an amicus brief with the United States Court of Appeal for the Seventh Circuit urging the court to strike down a Wisconsin statute that required certain individuals—including individuals who already fully served their criminal sentences—to wear GPS ankle bracelets every day for the rest of their lives.

Wisconsin enacted Wis. Stat. § 301.48 back in 2006. The law, among other things, imposed lifetime GPS monitoring on individuals who committed certain specified sexual violence offenses. The law applied to any person released from jail, prison, treatment, or involuntary civil commitment after January 1, 2008—regardless of the date of their offense, without any determination of their risk of recidivism, and even to those fully discharged from their criminal sentences.

Michael Belleau, who is represented by the ACLU of Wisconsin, sued the State of Wisconsin on the ground that imposition of lifetime GPS monitoring under the statute violated his rights under both the Fourth Amendment, which prohibits unreasonable searches and seizures, and the U.S. Constitution’s Ex Post Facto Clause, which prohibits states from passing laws that retroactively change the legal consequences of a crime or action. The district court agreed. It held that the state’s GPS tracking statute violated Belleau’s Fourth Amendment right against unreasonable searches and seizures and retroactively increased the punishment for a crime. The court also stated:

To hold that the State may . . . restrain the liberty of individuals it believes to be dangerous, not as punishment for a crime or as part of the care and treatment of the dangerous mentally ill, but as a civil regulatory scheme for the protection of the public, would significantly expand the power of the State [and] require[] a constitutional amendment.

Wisconsin appealed, and we filed an amicus brief urging the Seventh Circuit to uphold the district court’s ruling.

As we note in our brief, when law enforcement officials use GPS devices or other location surveillance technologies to systematically track where we are, they also learn an extraordinary amount of highly sensitive information about who we are. This is especially true given the accuracy of GPS technology; some of the GPS devices now available for purchase are advertised to be accurate within mere centimeters. In this way, 24-hour, lifetime GPS surveillance functions as—in the words of one article, which the manufacturer of the ankle bracelets used by Wisconsin approvingly republished on its website—a “prison without walls.”

This violates the Fourth Amendment, which as we outline in our brief, protects location privacy. As well tell the Seventh Circuit:

By allowing the state to monitor a person’s movements minute-by-minute throughout each day for the rest of [their] life, [Wisconsin’s] GPS surveillance program severely and pervasively invades [their] privacy interests.

And because the statute subjects individuals to GPS surveillance after they are fully discharged from their sentences, it’s a form of retroactive punishment prohibited by the Constitution.

We hope the Seventh Circuit agrees.