Seeing some of David Spragg's sample chips marked with the radio freequency they respond to caused me to read up a bit on the subject. Here is a link to an article from several years ago quoting John Kendall of Chipco on the technology and how it might be used in a casino.

Interesting that Wynn uses an older technology with a lower frequency on their tables and cage windows. 13.56 MHz seems to be the current preferred frequency for most RFIC applications.