Why the tinfoil? The transponders, also known as radio-frequency identification (RFID) tags, can theoretically send their contents to readers as far as 15 feet away unless they´re shielded by metal. Privacy advocates worry that thieves could use their own readers to secretly swipe your data. But Frank Moss, deputy assistant secretary of state for passport services, says the new passport´s cover will act as a shield, protecting the chip when the book is closed. Even when it´s open, Moss says, the chips will have a broadcast range of only about 10 centimeters and the data will be guarded by an encrypted digital signature.