Actually, this is something of a new problem in privacy considerations - broader than the strict "is a GPS device on my car illegal" question. A great deal of

Actually, this is something of a new problem in privacy considerations - broader than the strict "is a GPS device on my car illegal" question. A great deal of what we call "privacy" - in the common English meaning of the word, rather than the legal definition - consists of other people lacking information about our movements and actions. However, in that meaning, most of our privacy comes from the fact that 1) nobody is actively attempting to gather information and 2) it would be very difficult for them to do so if they tried. With technology, it is both dramatically easier to collect information, and dramatically easier to convert that information into a usable form (whether for sale, or for leverage in a government action). So although it's true that the technological method by which the FBI gathers information normally does not affect their legal right to do so, the standards under which the FBI operates were made when gathering information was difficult enough that stricter standards were not required. That's why it's a big deal. Normally they wouldn't bother to follow him. Normally they wouldn't have the time or money. As such, it was OK to give the FBI broad freedom to follow someone in an unmarked car, because the check on the FBI's ability to abuse that authority was its lack of money and manpower. Now that technology has solved the FBI's lack of money and manpower, the legal question is much more relevant.