If you should ever be forced by a robber to withdraw money from an ATM machine, you can notify the police by entering your Pin number in reverse order. For example if your Pin number is 1234 then you would key-in 4321.
The ATM recognizes that your pin number is backwards from the ATM card you placed in the machine slot. The machine will still dispense the money you requested, but unknowingly to the robber is that, police will be immediately dispatched to help you.
This information was recently broadcasted on TV and it states that it is seldom used because people don't know it exists.