My wallet has RFID protection, and I tested that my debit and credit cards cannot be read by the readers (vending machine, supermarket, vendors etc.).
However, my student ID can be scanned and read through the wallet. (It sits behind a credit card, so it’s not in a section without RFID protection.) How is this possible?
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Many proximity cards (especially HID branded ones in my experience) use a different frequency than the 13.56 MHz used for NFC and contactless credit cards.
For example, some HID branded prox cards use a 125khz band, US passport cards use 900mhz band
It could be possible that a sleeve was only designed to mitigate only certain frequencies.
Some RFID protection can be imagined as talking to someone else while having big cushions over your ears. If your partner is just loud enough, your environment is absolutely silent and/or your hearing is great you will still be able to understand your partner when the conditions are right.
It helps to understand how RFID works.
The card doesn’t have a battery, it essentially acts like a mirror. It reflects specific frequencies, and can add variation to the reflected signal.
So the reader broadcasts RF energy, this enters the card & is rebroadcasted but it is not exactly the same signal after it comes back from the card.
RFID blocking can attempt to direct the signal from the reader away from the cards using something like a metal plate, or what is essentially another card that creates a second (or more) reflected signals and confuses the reader.
Either way the blocking method needs to be designed for specific frequencies, and not all cards use the same frequency. Your student ID card might use a frequency that pases through the metal plate, or doesn’t interact with the ‘extra card(s)’.
RFID blocking can also be overcome by using a more powerful reader under ideal conditions, for example in an area with very little RF noise on the card frequency.
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