Write a secret message or use the regular black ink pen--this pen does it all! This invisible ink pen lets you write messages without leaving a trace. Use the pen's imbedded black light to read what you wrote. Kids love using this for writing secret notes or for diaries. Measures 5" long. Batteries included. Features ink made of special high-brightness compounds that are invisible to the naked eye, but magically illuminate when exposed to a black light. Conveniently located on the opposite end of the pen, the black light allows you to read any marks that you have made.