So this guy takes his car into the shop and the mechanics find this mysterious object stuck up next to the exhaust pipe. What is it? It turns out that it's a Guardian ST820, a GPS tracking unit used exclusively by the army and law enforcement. Awkward!
The guy in question's late father was apparently involved in the Muslim religious community and picked up some FBI interest. He's since passed away, but I guess the FBI thought it was worth tracking his kid, too.
Now, this is apparently legal in a few states without a warrant, but it should make it to the Supreme Court before too long. And I wouldn't put money on it staying legal. But until then, you might want to check under your car for anything out of place.