Just as personal checks replaced the use of cash, debit cards have replaced personal checks. Debit cards are beginning to be replaced by smartphone applications that securely enable cash-less transactions with a tap of the phone. Hard currency is playing a diminishing role in our modern economy. The ways in which money is exchanged in modern society depends upon a complex system of electronic fund transfers. For the sake of simplicity, we're going to refer to all of these electronic transactions simply as "wire transfers."