Counterfeit Detector PenSpecially formulated to detect bad bills, this counterfeit pen features technology that reacts to a key ingredient present in papers not used by the U.S. Treasury Department. The ink marked on a suspect, counterfeit bill will change in color from golden brown to blue-black. Authentic bills will not produce an ink color change. The pen is effective on all U.S. currency, including the new designs. Counterfeit Bill Detector Type: Pen; Counterfeit Indication Mark: Golden Brown;Blue-Black.