In good old days the spies used invisible inks that were applied to writing surfaces with a specialty purpose stylus, stamp, fountain pen, toothpick, calligraphy pen or even a finger dipped in the liquid. Once dry, the written surfaces looked as if they were blank, with a similar texture and reflectivity as the surrounding surface.
The documents were later made visible by different methods according to the type of invisible ink used such as heat or by application of some appropriate chemicals.
Well that was serious business. Here we are talking about a toy pen that can write and read invisible messages. The pen ha two tips—one tip for invisible ink writing, and another tip for decoding and developing the text via black light.
Besides having fun with friends and family, the pen can also be put to some practical use. The fluorescent that glows when illuminated with a UV light can be used to invisibly mark valuable household items in case of burglary, hence it can act as a crime countermeasure.
This invaluable Spy Pen is only $10.95. [Buy It]
