RSA Security - The Blocker Tag: Selective Blocking of RFID Tags for Consumer Privacy: Clever scheme for allowing consumers to block scanning of tags on items that they have purchased (eg, while in public places), and allowing scanning of those same items when desired (eg, in a medicine cabinet or refrigerator at home).
"One may think of a the RSA® Blocker Tag as "spamming" any reader that attempts to scan tags without the right authorization. (The RSA® Blocker Tag manipulates the reading protocol with the aim of making the reader think that RFID tags representing all possible serial numbers are present.) When a Blocker is in proximity to ordinary RFID tags, they benefit from its shielding behavior; when the Blocker tag is removed, the ordinary RFID tags may be used normally.
Thanks to their selective nature, RSA® Blocker Tags are designed not to interfere with the normal operation of RFID systems in retail environments. They help prevent unwanted scanning of purchased items, but do not affect the scanning of shop inventories. Thus RSA® Blocker Tags are designed not to be usable, for example, to circumvent theft-control systems or mount denial-of-service attacks -- only to protect the privacy of law-abiding consumers." 9:53:04 AM