How the Counterfeit Detection Marker Works:
The counterfeit detector pen is extremely simple. It contains an iodine solution that reacts with the starch in wood-based paper to create a black stain.
When the solution is applied to the fiber-based paper used in real bills, no discoloration occurs.
The pen does nothing but detect bills printed on normal copier paper instead of the fine papers used by the U.S. Treasury.
The key to avoiding fake money is to know your money: