Product DescriptionLike an ordinary twist ballpoint pen. A pen that James Bond would be proud to carry in his shirt pocket. One end of the Magic Spy Pen writes with invisible ink, the other end is a ultraviolet light which makes it visible. When your secret messages, codes, diagrams, etc. are written with this pen they will be invisible to the naked eye. The message can only be seen by shinning an ultraviolet light on the seemingly blank sheet of paper. This pen can also be used to mark your valuables with your name and phone number. If the marked items were ever stolen police could easily detect, identify, and return them. This pen will mark all surfaces including glass, paper, wood, plastic, and cloth. 4 LR41 batteries included. 0.5 oz x 5.25 in.