Kim Zetter at Wired's Threat Level reports an important and fascinating story today about Kathy Thomas, an environmental and animal rights' activist, who the FBI tracked with a GPS device. Thomas found the tracker under her car after she noticed that agents had stopped following her around.
Thomas gave Wired the device, who handed it off to iFixit for the "first-ever dissection of an FBI tracker." You can watch a video of the process above.
The Constitutionality of such surveillance is in question, as Zetter notes, but it's clear that law enforcement officials aren't waiting for a high court ruling to use the technology.