"All passports issued by the US State Department after January 1 will have always-on radio frequency identification chips, making it easy for officials – and hackers – to grab your personal stats. Getting paranoid about strangers slurping up your identity? Here’s what you can do about it. But be careful ..."
"4) The best approach? Hammer time. Hitting the chip with a blunt, hard object should disable it. A nonworking RFID doesn’t invalidate the passport, so you can still use it."
from Jenna Wortham: How To: Disable Your Passport's RFID Chip