A '''counterfeit banknote detection pen''' is a pen used to apply an [[iodine]]-based ink to [[banknote]]s in an attempt to determine their authenticity.
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==Background==
Counterfeit banknote detection pens are used to detect [[counterfeit]] [[Swiss franc]], [[euro]] and [[Federal Reserve note|United States banknotes]], amongst others. Typically, genuine banknotes are printed on paper based on cotton fibers and do not contain the starches that are reactive with iodine. When the pen is used to mark genuine bills, the mark is yellowish or colourless.
Such pens are most effective against counterfeit notes printed on standard printer or [[photocopier]] paper.<ref>{{cite web|url= http://money.howstuffworks.com/question212.htm |title=How does a counterfeit detector pen work? 123 | work=HowStuffWorks |accessdate= 2008-03-28}}</ref> The chemical properties of US banknotes prior to 1960 are such that marking pens do not work.<ref>{{cite web
