Both I and my younger son have had this happen with our bank debit cards over the last couple of years. We got together with a friend who works for our bank in the card fraud department and started looking for a pattern. We noticed that every time the bank caught an irregularity and shut down the card (note: it was always rapid, and detected within a few hours) it was after using the card at small, out of our normal area gas stations. The lady at the bank said most of those type gas stations use wireless, wi-fi style systems for card transactions and it makes it easier for thieves to sit across the street (or in some case inside the store) and snatch card info. Most of the bigger fuel centers use hardwired systems.