Cheapest I've seen this, Argos is currently £22 and ebay £40+
Your secret is safe with the Superhero Girls Electronic Secret diary. Use the magical pen to write down all your secrets and close the Diary to keep them safe! If you want to read the secret messages, open the diary up using the special electronic key fob and shine the key fob light onto the message to make it appear. Don't worry, no one else will be able to sneak a peek at your secrets, the diary's alarm will activate when anyone but you tries!
Electronical diary and key fob opening system.
Invisible ink pen and a key fob with ultraviolet light.
Alarmed diary prevents intruders.
Requires 3x AAA batteries.