Counterfeit detector pen delivers ink that reacts to printer copy paper so you don't have to take a chance on accepting large counterfeit bills. Pen is easy to use and requires no training. The iodine in the ink reacts to starch leaving a dark brown or black mark. Pen will leave an amber mark on fiber-based paper used in authentic currency. Antimicrobial technology is designed to inhibit bacterial and fungal growth on the pen's surface. Cap prevents pen from drying out. For best results, use in conjunction with other counterfeit detection methods.