Why an ATM kept the card instead of just ending the session
A PIN is a check that the person using a card knows its secret number. After repeated failures, an ATM could respond in two ways: stop the transaction, or physically retain the card. Retention was a stronger form of containment. If the card had been stolen, the thief could not simply take it away and keep guessing at another machine.
That choice depended on the ATM’s card-handling hardware. The reader could draw a card inside and route it into a secured compartment rather than send it back through the slot. In everyday speech, people said the machine had “swallowed” the card; mechanically, it had taken custody of it.
Security bought with a costly inconvenience
The machine could not reliably tell whether the failed attempts came from a thief or from the legitimate owner mistyping. So the same safeguard applied to both. Once the card was inside, the customer generally could not retrieve it at the machine; getting it back meant dealing with the bank branch responsible for the ATM.
That was the tradeoff: the machine protected a potentially compromised card by making it unavailable even to its owner. A locked transaction could be retried later with the card still in hand. A retained card turned a brief mistake into a recovery problem involving the bank and the machine’s secured contents.
