Powerful yet compact ultraviolet penlight reveals UV-sensitive security markings on 1996 series or newer U.S. currency denominations greater than $1. Counterfeit detector pen detects bad bills by marking a line on the bill; if the mark turns dark, the bill is suspect. UV light also works on many foreign currencies, major credit cards, passports, traveler's checks and more. ™. Currency: USD & Most International Currencies; Number of Methods: 2; Counterfeit Verification Methods: Chemical/Ink; Ultraviolet (UV); Ink Color (Legitimate): Amber.