Stallman is no fan of RF IDs because they hold personal data as securely as a sieve holds water. He was miffed that RF ID cards were being used despite promises at the last UN conference in 2003 that they wouldn't be.
He bought an entire roll of aluminium foil and wore his foil-shielded pass prominently and unwrapped it to go through any of the check-points.
During his keynote speech Stallman gave a moment's talk about the RF ID issue, and passed his roll of aluminium foil around the room for others to use.
Soon everyone was shielding their passes and afterwards Stallman was taken aside by UN security who refused to let him leave the room to talk to press, because he was flouting their security measures.
Apparently it took a fairly high level shouting before Stallman was allowed to continue with his series of speeches.
You can read all about it in an eye witness bog by Stallman's mate Bruce Perens here. µ