Mine came with two free pens for swiping bills (a black color is bad)

Superior Protection Against Counterfeiters. Two tests to assure that you are accepting only authentic US currency. Pen tests the paper. UV light reveals embedded security markings.
UV Light can also be used to validate drivers licenses, credit cards, passports, international currency, government documents and more.
Light Uses 3 replaceable button cell batteries (included) available everywhere. When the pen runs out of ink simply replace it with a new one.