Highly effective and inexpensive tool for detecting bad bills. Simply make a small mark on U.S. currency. Chemically sensitive ink works instantly. An amber mark passes the test, while a dark brown or black mark fails, meaning the bill is likely counterfeit. Works on all new design U.S. currency (bills series 1959 and later). Powerful LED with ultraviolet light cap is highly effective on U.S. and foreign currencies, passports, credit cards, cashiers checks and money orders. 3 LR44 cell batteries included. Counterfeit Bill Detector Type: Pen; Marking Color: Amber; Counterfeit Indication Mark: Black; Dark Brown; Currency: U.S. and most foreign currencies.