Radio frequency identification (RFID) tags -- tiny devices that broadcast data about any object in which they're embedded -- have been proposed as a way of improving inventory control in San Francisco's library system. A librarian writes that "RFID allows a person to pass a wand over the shelves, and the wand will beep when it finds a book out of place. Of course, RFID would allow one to wand a dormitory to find out which rooms contain library books. Or, maybe, we want to know which dorm rooms do NOT contain library books. For the really paranoid, we could equip a helicopter to fly over the city, to look for library call numbers relating to WMD."
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