Genie 11794 counterfeit bill detector Blue, Yellow

Handy money checker; Portable and uncomplicated protection against counterfeit money; Euro checks, US dollars, British pounds, Swiss francs.
How it works: use the pen and mark the bill, preferably in a light place on the edge of the bill and wait a moment.

Result:

Real money - the line fades to a slightly yellowish colour and is hardly visible at a later date.
False Money - The line is very dark and very clearly recognizable
Banknotes consist of specialty paper - the pen recognizes it by the composition of its ink, which then fades. Counterfeit money often consists of plain paper, the ink reacts and becomes dark.