When you have more than two RFID Cards such as credit card like "PayPass" or "PayWave", RFID Commuter Pass or RFID ID Card. You should have this product to prevent RF interference. Place it between two cards so that you can use your RFID Card without Interference error. and just wave the wallet or card holder in front of the RF Card Reader. You don't need to take RFID Card out each time.