Hide your messages from spying eyes with this Secret Love Letter Invisible Ink Writing Set. The ink is completely invisible in normal light and the secret message can only be revealed by using the ultraviolet light located in the pen cap. This beam consists of UV energy which causes particles within the ink to illuminate ad reveal the message. There are 2 pens per set. Comes packaged in a hanging blister card - the light button can be pressed to preview a secret message inside the packaging.