The FBI has been placing GPS transmitters on the vehicles of individuals they suspect are criminals or terrorists without warrants.
This criminal activity came to light when Yasir Afifi, a 20-year-old computer salesman and community college student, took his car in for an oil change in 2010. The mechanic spotted an odd wire hanging from the undercarriage. They removed it from the car, posted images of it online and asked for help in identifying it. FBI agents paid Mr. Afifi a visit at his home and demanded the return of their property.
One federal judge wrote that the widespread use of the device was straight out of George Orwell’s novel, 1984. “By holding that this kind of surveillance doesn’t impair an individual’s reasonable expectation of privacy, the panel hands the government the power to track the movements of every one of us, every day of our lives,” wrote Alex Kozinski, the chief judge of the 9th U.S. Circuit Court of Appeals. This sane statement was part of his condemning dissent in which a three-judge panel from his court ruled that search warrants were not necessary for GPS tracking.
The Obama Administration asked the D.C. federal appeals court that ruled it was unconstitutional to plant GPS transponders on vehicles with warrants to change its ruling. It argued that investigators will lose access to a tool they now use “with great frequency.” 
 Yahoo News. “Oil change reignites debate over GPS trakers,” 10.16.2010.