Passive radio location and broadcast stream decoding of the gsm announcements made by the phone, should be feasable, i dont see why the phone has to be tricked

Passive radio location and broadcast stream decoding of the gsm announcements made by the phone, should be feasable, i dont see why the phone has to be tricked into a conversation with a fake cell tower to locate it. Under those circumstances would it still be a search, is it not the same as the owner of the phone wearing an audio system that broadcast loudly thier name. See:http://www.rtl-sdr.com/receiving-decoding-decrypting-gsm-signals-rtl-sdr/ http://www.rtl-sdr.com/receiving-decoding-decrypting-gsm-sig...