The secretive technology is generically known as a stingray or IMSI catcher, but the Harris device is also specifically called the Stingray. When mobile phones — and other wireless communication devices like air cards — connect to the stingray, it can see and record their unique ID numbers and traffic data, as well as information that points to the device’s location. By moving the stingray around, authorities can triangulate the device’s location with much more precision than they can get through data obtained from a mobile network provider’s fixed tower location.
The government has long asserted that it doesn’t need to obtain a probable-cause warrant to use the devices because they don’t collect the content of phone calls and text messages but rather operate like pen-registers and trap-and-traces, collecting the equivalent of header information.

via Florida Cops’ Secret Weapon: Warrantless Cellphone Tracking | Threat Level | Wired.com.