Accurate and affordable! The DTEK counterfeit pen is the classic screening tool as your first line of defense before moving on with other methods of counterfeit detection. A point-of-sale register with a visible counterfeit detection device is much more likely to deter individuals from attempting to use counterfeit bills. Ink changes color depending on the authenticity of the currency. Amber indicates legitimacy, while black or brown identifies it is counterfeit. Good on all U.S. currency 1959 and after. Antimicrobial protected, prevents the growth of odor-causing bacteria and fungus on the surface of the pen.