Decoder pen
The decoder pen, yes-no pen, yes-know pen or magic pen book is a combination of decoder pen or
However, the pen and paper can be damaged easily if excessive rubbing is used. Therefore, most invisible ink books contain an advisory saying to use a very gentle back and forth motion - not a circular grinding motion, when using the books.[citation needed]
Fans of the adventure games released by Sierra Entertainment in the 1980s such as King's Quest and Space Quest are also familiar with the decoder pen, which was used to reveal the answers to hints in the hints book sold for each game. Eventually these were replaced by a colored translucent plastic window, which eliminated a visually interfering red pattern.
References
- ^ "Confidential Secret Decoder Pen". Archived from the original on 15 August 2013. Retrieved 24 August 2013.
External links
- Lee Publications (publisher of invisible ink books)
Note: there is a warning about theft of information when accessing this link 26/11/2021.