From WNYC in New York, this is On the Media. I'm Brooke Gladstone.

And I'm Bob Garfield. This week, a 20-year-old California college student named Yasser Afifi took his car in for an oil change.

There, mechanics found a strange device attached by magnet to the undercarriage, a device called an Orion Guardian ST820.

That's a GPS tracking device that had been placed there by the FBI as part of a terrorism

investigation.

Agents this week found themselves in the embarrassing position of demanding that Afifi

return their super double secret gizmo. He did. But what about satellite tracking

in American citizens every movement? Is it legal? Do authorities need a warrant? At the moment,

that depends on where you live. Aran Kerr is a law professor at George Washington University,

where he's been following this issue.

Aran, welcome to the show.

Thank you.

Let's start with the recent California Circuit decision.

What happened there?

That was a case in which the government wanted to monitor the location of a person who the government thought was involved in growing marijuana.

And so the government installed a GPS device

about the size of a bar of soap on the suspect's car in his driveway.

The government used that information to show that he was, in fact,

near where the marijuana was growing

and to show his involvement in the crime.

It worked like a charm, in fact,

but the defendant appealed on the grounds that the tracking

...