This gear ring has a small cavity that allows you to store an RFID Capsule in it. The Capsules are able to be added to a 125 Khz system. Below is a link to the RFID badges on sparkfun. This project was based on an idea by Daniel Goncharov of ZeGo Robotics.

https://www.sparkfun.com/products/9416

The ring is printed on a Makerbot Replicator 2 and the capsul is inserted in the side hole. Gel Set superglue is used to hold it in place. Once the capsule is in the ring, you can scan it into whatever RFID system you are using.