Hello.
For the entire project on both sides I suggest the following hardware:
-2x microcontrollers arduino (You can use only the chips not the entire arduino board to save space and reduce power consumption - atmega328, atmaga32u4, ATtiny, etc)
-2xRFID readers can be any (RDM6300, ID-12LA) on 125KHz or MFRC522 on 13.56MHz
-multiple tags and/or badges based on the RFID reader you choose, they need to be compatible
-2xvoltage regulators or dc-dc converters that support input on 24V and output on 5V (to power both controller and rfid reader) (They need to be picked after choosing the rfid readers so that they can supply enough current) (Alternatively if you want to use the full arduino board and then power the rfid reader from the onboard regulator you need a regulator from 24V to 7-12V, but you cannot power it directly from 24V because it cannot handle that voltage)
-2xLED`s or buzzers for outputting the status of a successful or failed read
-Considered that the reader will be outside the electronics should be fitted inside boxes that will not allow water, moisture and other to effect or damage them
That's it regarding hardware in the next steps I will provide all the code, schematics, instructions and debugging needed to complete the project.
Feel free to contact me if you want so we can discuss more.
Best regards,
Mihai