Problems with fraudulent banknotes‎,‎ This Money checker detector pen is suitable for all currencies‎.‎ Mark a bank note With a genuine note ‎- the pen ink will turn a clear to yellow colour‎,‎ which will then either vanish completely or leave a clear mark after a short time depending on the temperature‎,‎ A potential forged note ‎- the pen ink will turn a brown to grey colour which will remain on the notes‎,‎  Potentially forged notes should be checked with an additional device such as a bank note testing machine at your local bank‎.‎