Pack of 5 G-Star Technology Counterfeit Detector Pen Marker Set Selling One Blister Pack which contains five (5) counterfeit detection marker The ink in this pen marker is designed to react to the unique chemical compound present in the US bills The pen marker is 5.25" long, the blister pack measures 10" X 4.5" X 0.5" The ink stays yellow on genuine bills and changes to dark color on counterfeit bills The ink will disappear in a few hours