Last month the phone company sent me a new card for my phone. I don't remember all the benefits they claimed but determining my location was one 'safety feature'. All I had to do was install the new card and the police would be able to locate me if I ever called 911 and asked for help.
I figure that since I don't drink enough to get drunk I alwasys know where I am. I'll keep the card in the drawer.
That's not an RFID device. It's software that tells not only which tower you ping to, but which side of the triangular array you connect to.
So the police, when you dial 911, can locate you within a particular region of a cell.
You're lucky to get it on a card- many carriers just upload new software to your phone without telling you.