Today the Supreme Court "checks in" on police use of a technology that carries the gravest possible privacy consequences. While I doubt the Justices use Foursquare or any geolocation service to disclose their whereabouts, they will hear arguments about whether police can use GPS to track the movements of citizens over extended periods of time without getting a warrant.

• Supreme Court to decide if police may use GPS tracking devices without a warrant

• Government claims tracking public movements not a search

• Privacy and civil rights advocates say rights of privacy, association at risk

A Tale of Two Trackings

The Court has agreed to settle the conflicting GPS decisions issued by two federal appeals courts.

On the west coast, DEA agents used a GPS device to track the comings and goings of Juan Pineda-Moreno. On two occasions they entered his property to attach the device to his vehicle in his driveway. He was convicted with evidence this tracking helped obtain. The California-based federal 9th Circuit Court of Appeals, often maligned for its supposed liberal bias, upheld his conviction.

On the east coast, Antoine Jones of Washington, DC, was sentenced to life in prison for a drug trafficking conviction obtained with the help of a GPS tracker. Police attached it to his vehicle and monitored his movements for a month. They searched places he frequented and found drugs and money there. The federal Court of Appeals for DC overturned Jones' conviction, saying the warrantless tracking violated his Constitutional rights. (It's ironic, but the police actually got a warrant to use the device. They didn't start using it though until after the warrant had expired. Such are the makings of important Constitutional decisions.)

And this is an important decision, which the Supreme Court will make after considering today's arguments. To New York civil rights lawyer Susan J. Walsh, it may be "the most important privacy decision the Court will make in my lifetime."

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