Nope, an EM4100-compatible card (or a key fob) is just a 64-bit ROM with radio interface. You can read its value and replay it to a reader; the latter won't be

Nope, an EM4100-compatible card (or a key fob) is just a 64-bit ROM with radio interface. You can read its value and replay it to a reader; the latter won't be able to tell the difference between the original card and your spoofed one. Better (and more expensive) RFID tags may have an encrypted communication protocol.