Why does the auto teller machine refuse my ATM card in one direction, and allow it in the other direction. I know why, to read the strip, but I don’t know how it knows. Any ideas?
if the magnetic pickup or whatever to read the strip is on the LEFT side on the bottom, then it cant read the strip if you put it in any other way…
like the machines where you slide the side of the card through at a supermarket, if you slid the card while holding the magnetic strip part in your hand, the reader sees nothing but plastic, you might as well slide a piece of paper in there…
I believe that it gets blocked by the raised numbers on the card if you try to put it in the wrong way or upside down. The slot on the machine is designed so that the clearance to the slot will only allow the numbers to go in one way.
On some machines there is also a mechanical block that will pop up if you attempt to put the card in and the machine does not detect the magnetic strip right away. If you’ve got a dirty magnetic strip that doesn’t always register the first time, those things can be a real PITA.
There’s a sensor just inside the slot that detects the mag stripe.
If the sensor sees a stripe, a gate opens inside the card reader and rollers pull the card into the reader where a track reader (much like the heads in a cassete deck) reads the account info on the card. The gate closes once the card is in the reader - this prevents card-on-a-string, or dummy card wired to a computer (as in War Games fraud attempts.