How is it possible to activate a credit card by tapping it against one’s phone?
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Embedded in the plastic around the card’s chip is a thin, coiled, foil radio antenna. The antenna’s length makes it resonant for the radio frequency at which the RFID reader operates. The radio signal itself induces enough current in the antenna to operate the chip, which replies to the RFID signal with its own radio transmission that supply’s the card’s information.
The low power of the card’s reply signal means the card needs to be right next to the reader.
The most reliable way to tap a card is with the chip near your hand, placing the antenna right over the card reader.
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