How Contactless ATM Cards Work Without a Battery When you tap your bank card on a POS terminal or an ATM, it feels almost magical. There is no visible power source on the card, yet it powers up, talks to the machine, and completes a secure transaction in under a second. The reason this works is simple but elegant: the card is passive . It does not have a battery. Instead, it harvests a tiny amount of energy from the electromagnetic field generated by the payment terminal. What Actually Happens When You Tap When you bring your contactless card close to a terminal, the two devices communicate using a technology called Near Field Communication (NFC) , which typically operates at 13.56 MHz over a very short distance (a few centimeters). The terminal generates an alternating electromagnetic field around its reader. Your card enters this field and couples to it using a small coil antenna inside the plastic. This coupling allows the card to draw just enough energy to power it...