The following information is for the readers of our book Switch Craft. However, if you are interested in making your own privacy passport cover, key card holder, or wallet that may prevent unwanted RFID (radio-frequency identification) sniffing, you are welcome to read on.
In Switch Craft we show our readers how to sew together a simple yet attractive passport cover with aluminum foil lining. You may apply the same technique to create other privacy protecting accessories to hold your RFID embedded items. Please do note that the effectiveness of this measure depends on various factors, such as thickness of foil, distance to the RFID reader, and radio power of the reader. If you wish to be ultra safe, throw in an extra layer of foil (or two) while you are at it.
As you may have noticed, RFID technology has become quite common. It is in the U.S. passport, in those contact-less key cards that let you get in and out of buildings, and in many credit cards as well (marked "PayPass," "ExpressPay," "payWave," "blink," etc.). Granted, the chance of someone hacking into your credit cards isn't high. But as this Boing Boing TV video has demonstrated, someone can potentially obtain cardholder name and card number using a $8 reader.