In this talk, we present the first open source implementation of HID SEOS communication protocol over RFID. HID SEOS is a credential technology designed to provide enhanced security, flexibility, and convenience for access control and identity management applications. It's currently the leading access control solution for HID Global and is widely used in corporate, educational, healthcare, and government settings.The documentation for this card technology is not publicly available so no previous open source implementation exists.We will demonstrate how it works and give insights in our process of making this project happen. The source code has been incorporated into the Proxmark3 project.