http://online.wsj.com/article/SB10001424053111904194604576583112723197574.html

JENNIFER VALENTINO-DEVRIES

For more than a year, federal authorities pursued a man they called simply "the Hacker." Only after using a little known cellphone-tracking device—a stingray—were they able to zero in on a California home and make the arrest.

A Harris StingRay II, one of several devices dubbed 'stingrays.'

Stingrays are designed to locate a mobile phone even when it's not being used to make a call. The Federal Bureau of Investigation considers the devices to be so critical that it has a policy of deleting the data gathered in their use, mainly to keep suspects in the dark about their capabilities, an FBI official told The Wall Street Journal in response to inquiries.

A stingray's role in nabbing the alleged "Hacker"—Daniel David Rigmaiden—is shaping up as a possible test of the legal standards for using these devices in investigations. The FBI says it obtains appropriate court approval to use the device.

Stingrays are one of several new technologies used by law enforcement to track people's locations, often without a search warrant. These techniques are driving a constitutional debate about whether the Fourth Amendment, which prohibits unreasonable searches and seizures, but which was written before the digital age, is keeping pace with the times.

On Nov. 8, the Supreme Court will hear arguments over whether or not police need a warrant before secretly installing a GPS device on a suspect's car and tracking him for an extended period. In both the Senate and House, new bills would require a warrant before tracking a cellphone's location.

From the blog:

The exact way these stingray devices work is one of the big questions in a case currently playing out in U.S. District Court for the District of Arizona. The defense in that case wants to know just how the stingray was able to locate a mobile broadband card in an apartment building. The card was key in the later arrest of the defendant on fraud charges.