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, travelers checks and more. Counterfeit Bill Detector Type: UV Light and Watermark Detector; Color Change Ink; Marking Color: Amber; Counterfeit Indication Mark: Black; Dark Brown; Currency: U.S.