I don't know how it works on a computer, but my bank offers a simlar "duress" PIN#. Let's say my ATM card's normal PIN# is 1234, the duress PIN# is 4321. If someone holds a gun to my head and demand that I give them the PIN#, I can just give 4321 and the ATM card. With the 4321 code, it will allow the robber to draw around $300 in US dollars and the receipt will show "account overdrawn" after that. (so the robber/kidnapper can't continue to draw money from it) Not sure if US banks offer this type of ATM card?