The enclosing aluminum plates serve an electronic defense purpose by forming a continuous conductive perimeter that mimics a small Faraday cage. Tests using standard 13.56 MHz RFID readers, the frequency utilized by modern contactless payment chips and tap-to-pay smartphones, show zero signal transmission through the plates. This layer prevents unauthorized skimming attempts in densely populated transit hubs and airports.
Security capabilities change when dealing with low-frequency signals. Many enterprise employee badges, parking gate fobs, and apartment entry systems operate on the 125 kHz band, which penetrates thin aluminum barriers with relative ease. A tap-and-go metro card nested inside the outer pocket of this RFID-blocking cardholder will fail due to frequency interference, requiring users to partially slide the card free from the frame to register at turnstiles.
