Stingray cellphone tracking device designed to locate mobile phone even when not being used to make a call.

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.

via online.wsj.com

Stingray works by mimicking a cellphone tower, getting a phone to connect to it and measuring signals from the phone.
It lets the stingray operator "ping," or send a signal to, a phone and locate it as long as it is powered on

U.S. armed forces also use stingrays or similar devices, according to public contract notices. Local law enforcement in Minnesota, Arizona, Miami and Durham, N.C., also either possess the devices or have considered buying them, according to interviews and published requests for funding.

The sheriff's department in Maricopa County, Ariz., uses the equipment "about on a monthly basis,"

Experts say lawmakers and the courts haven't yet settled under what circumstances locating a person or device constitutes a search requiring a warrant.
Tracking people when they are home is particularly sensitive because the Fourth Amendment specifies that people have a right to be secure against unreasonable searches in their "houses."