Pen can detect forensic substances such as Smartwater and SelectaDNA. This innovative Counterfeit Detection Pen works on both paper and polymer notes due to the integral 365nm UV bulb within. The pen works on all paper notes by marking the currency and showing a clear mark to determine a genuine note and a dark mark to indicate a counterfeit. However, the UV light means it can be shone over both paper and polymer notes to detect the hidden UV features within genuine currency. Pen can also detect forensic substances such as Smartwater and SelectaDNA.