RFID codes that pass the CRC check should show up in the serial monitor.
You can get the raw output by using the command monitor serial.
I assume you also gave the RFID reader power? (hook it up to BATT+ or 3.3v, not the 5v pad)
Have you tried plugging in a LED to pad 4 on the reader? It should blink when something is scanned.
I haven’t tried it with the antenna from the savi, so there could be an incompatibility there.