To become a detective or spy is more fun game, unleash you child's hidden talents with this magical spy pen Write Your Secret Message with This magical invisible ink pen ,once your secret message has been written with this invisible ink pen, wait a few seconds to shine the light from the pen's cover and reveal the secret of the secret message. ultra violate light from back of the pen is used to read the secret massage, also can be used to detect fake currency. pack of spy pen Interesting option for birthday return gifts