Metal detector knows how much cash is in your wallet

[snopes]

It has long been an urban legend that the security strips found in US banknotes let shadowy government agencies use metal detectors to track how much cash you are carrying.

Even though the strips are made of plastic, the legend is so pervasive it once made an appearance in an episode of TV series The X-Files. Now it seems the conspiracy theory may have been half right: it is possible to both detect and count concealed banknotes printed with magnetic inks.

http://www.newscientist.com/article/...ur-wallet.html