Traditional access control cards are read-only, playback devices. When read, they simply send a fixed sequence, much like a bar code. With the right equipment, one may record the sequence and play it back. Traditional access control readers may fail under playback attacks.

Proximity smart card systems were designed to contain accounts and sensitive information. They have means to authenticate cards and readers, and they effectively detect and resist playback attacks.

Traditional access control cards will gladly spill their contents to any compatible reader. Just pass a card by and it will gladly reveal the entire content of that card.

Proximity smart card systems resolve this problem by sharing secret keys. Without these keys, other readers can't access the cards and other cards can't access the readers. They may be compatible but without the shared keys, they won't reveal their secrets. Modern, secure, micro-controller based readers allow you to change keys, which gives you final control over your readers and cards.