Musolesi said the researchers in their experiment had to sign waivers promising to not use the data to determine where the 25 volunteers lived. "It's just ethics that stops us doing this, as the data are there," he said. "You can . . . construct information about behavior — if he's in a movie theater, find out what he's seeing. It's quite fine-grained, so you can track shops. There are big privacy implications."
The Supreme Court's decision in January was narrow — dealing only with the issue of the police accessing the suspect's car without a valid warrant — and left open the broader question of what rules guide government collection of the personal location data.
The Sixth Circuit Court went further in its ruling last week, noting that previous court cases have established that information legitimately in the public domain — such as an individual's movements on public roadways — can be gathered by police in many situations. Improving technologies, the court said, are permitted to assist police investigations, even if criminals are not aware of the latest techniques.
"When criminals use modern technological devices to carry out criminal acts and to reduce the possibility of detection, they can hardly complain when the police take advantage of the inherent characteristics of those very devices to catch them," the court said.
The Drug Enforcement Administration, which was running the case, acquired a court order — although not a search warrant — to monitor the suspected drug runner's phone. But the court said neither may have been necessary for such cases. (One of the judges on the three-judge appellate panel said a warrant was needed.)
"We have two vague opinions and a lot of concern," said Orin Kerr, a George Washington University law professor following the issue. "At some point in the next 10 years, the Supreme Court is probably going to have to figure out how it feels about cellphone location information."