As the year draws to a close, EFF is looking back at the major trends influencing digital rights in 2012 and discussing where we are in the fight for free expression, innovation, fair use, and privacy. Click here to read other blog posts in this series.

EFF has long been fighting to defend your privacy in your physical movements. 2011 brought major developments around cell phone and GPS tracking in the courts and Congress. But that was nothing compared to 2012, which turned out to be a monumental year.

In January, the Supreme Court kicked off the year by issuing a landmark decision in United States v. Jones, a case that squarely presented the question of whether the Fourth Amendment requires the government to get a probable cause warrant to attach a GPS device to your car and secretly monitor your movements over time. EFF teamed up with a broad range of advocates and technologists—including the inventor of GPS himself—to file a friend-of-the-court brief urging the court to say "yes."

In its majority opinion, the court decided that planting a GPS device on a car is a physical trespass that requires a warrant, but dodged the question of whether the warrantless tracking itself would violate the Fourth Amendment. But in two concurring opinions, five of the nine justices said people have a reasonable expectation of privacy in their movements over time, and long-term location tracking without any physical trespass should require a warrant, too.

Since the Supreme Court's decision, lower courts continue to struggle with these questions. In cases involving GPS devices installed by the police before Jones was decided, courts are still admitting GPS evidence in jurisdictions where prior case law allowed the warrantless use of the devices. But as these older cases work their way through the judicial system, warrants should soon become the legal norm for police using GPS devices in their investigations.

Courts are also confronting the question of whether law enforcement officers need a warrant to track people's movements over time. In an encouraging development, the South Dakota Supreme Court (pdf) became the first after Jones to recognize a reasonable expectation of privacy in a person's movements, hinging its decision to suppress GPS evidence on both trespass and reasonable expectation of privacy grounds.

In federal courts, the issue has played out most directly in a series of cases where the government seeks records from cell phone companies to trace the physical movements of investigatory targets. District courts have been mulling over this question for several years—with varied results. In 2010 , the Third Circuit Court of Appeals held that magistrate judges have the discretion to make the police get a search warrant before obtaining cell phone location records, but didn't reach the question of whether the Fourth Amendment requires a warrant in such situations. This year, two federal appeals courts squarely confronted that question.

The Sixth Circuit Court of Appeals held in United States v. Skinner (pdf) that a person doesn't have a reasonable expectation of privacy in location data broadcast by a cell phone, so the Fourth Amendment doesn't require the government to get a warrant before using that information to monitor a person's real-time location. EFF and several other civil liberties organizations fought to convince the court to reconsider its decision, but it refused.

Over in the Fifth Circuit Court of Appeals, EFF joined the American Civil Liberties Union Foundation and the ACLU Foundation of Texas to file an amicus brief backing a judge's decision to require the government to get a search warrant before obtaining two months of cell phone location data about a suspect. We argued the case before the Fifth Circuit in October, and are waiting for a decision.

Indeed, the cell-site issue even came up in Jones after the Supreme Court sent the case back down to the trial court, since investigators had not only used a GPS device to warrantlessly track Jones' car, but had also obtained four months of cell-site data to track the location of Jones' phone—again, without a warrant. Jones moved to suppress the evidence with support (pdf) from EFF and the Center for Democracy and Technology. But just this month the district court dodged the key Fourth Amendment question, finding that the police demanded the cell-site data way back in 2005, well before the Supreme Court decided Jones. Since they had a good-faith belief that what they did was lawful at the time, the cell-site data could be admitted as evidence.

The courts aren't the only place where the battle over location privacy played out this year. State legislatures and Congress zeroed in on the issue, too.

In California, the state legislature passed SB 1434, an EFF- and ACLU-sponsored bill that would have required law enforcement to get a warrant before gathering location information from mobile devices and car navigation systems. Unfortunately, Governor Jerry Brown vetoed the bill this fall, dashing our hopes for greater location privacy protections on the state level.

In Congress, Senator Leahy introduced S. 1011, the Electronic Communications Privacy Act Amendments Act, which would generally require the government to get a warrant to collect geolocation information. And just this month, the Senate Judiciary Committee voted in favor of S. 1223, Senator Franken's Location Privacy Protect Act, which would require companies to inform and get consent from users before collecting or sharing their location information. We'll likely have to wait until 2013 to see whether these bills become law.

Next year promises to be even more interesting as the courts and legislatures continue to grapple with location privacy in the wake of Jones. Stay tuned.