snip
The ECB is in talks with Hitachi, whose 0.3mm "mu-chip" responds to radio signals by sending out a 128-bit number. This information could include a serial number and date and place of origin. It could also be used to track the note as it wends its happy way around the EU.
Sniped from:
http://www.theregister.co.uk/content/7/30850.html