Invisible Ink Pen with UV Light Marking Secret Message Spy Pen Detecting Counterfeit Banknotes it uses high brightness Invisible ink writing made of special UV-visible compounds This means that the ink in normal light Completely invisible under the near-visible spectrum. Flip the pen over, shine a light where the ink was applied and your hidden message will light up You can use it in different interesting occasions: secret messages, invisible tattoos, amazing signs in the dark, personal items, banknote detectors Package includes a pen and 3 * LR41 button batteries Invisible Ink Pen with UV Light Marking Secret Message Spy Pen Detecting Counterfeit Banknotes It is printed with invisible inks made from a special UV-Vis compound that is highly luminous, which means the ink is completely invisible under normal light close to the visible spectrum. Flip the pen over and the light will shine where the ink was used and your hidden message will light up You can use it in different interesting occasions: secret messages, invisible tattoos, amazing signs in the dark, personal items, banknote detector This package includes a pen and 3 years of 41*LR7 button batteries.