We have two models of Counterfeit Currency Detector Pens available. One is an ink pen that identifies simple counterfeit currency and where an ink mark is placed on the currency. If the ink remains yellow or disappears the currency is likely authentic. If the mark turns black then the currency is counterfeit. The second pen also include an Untraviolet light which will show the security thread in real currency and will show that there is security thread in the paper if the currency is counterfeit.