bigger than a soda can. in some states, law enforcement can stick a gps on your car while it's on your driveway and track almost every move you make. in yasser's case, it's not clear where his car was when the fbi placed a tracking device on it. a computer salesman in california removed the device when he found it. wasn't long before the fbi agents approached him asking pointed questions. >> have you been to yemen for any type of training. no. the agents asked for their gps back. afifi is not accused of wrongdoing. contacted by cnn, the fbi wouldn't comment on the case. but a spokesman said they don't need a warrant to track a vehicle with gps when it's in a public space. how watchful an eye can this device keep on you. >> where's the best place of that. >> the frame of the car, tore truck.