Compact "Pocket-Sized" Counterfeit Detector Pen detects genuine, U.S. currency paper. It is designed for fast-paced businesses like restaurants, banks, retail stores and entertainment venues. This currency-screening device is inexpensive and easy-to-use. Simply make a small mark on U.S. currency and examine the color. If the mark is clear/amber, the bill is genuine. If the mark is black/dark, the bill is probably counterfeit. Pocket-size pen will outlast and outperform others with three times the ink and fitted parts that ensure a long shelf life.