In this study, a dual frequency supported Radio Frequency Identification (RFID) card reader device that can operate at both 125 kHz and 13.56 MHz is developed for use in access control systems. Most of the existing systems operate at a single frequency band and therefore offer limited card compatibility. But, the proposed design supports multiple RFID standards and offers a more flexible and user-friendly solution. The reader functioning at 125 kHz can successfully detect cards based on the EM4100 protocol, whereas at 13.56 MHz, it effectively communicates with MIFARE Classic, MIFARE Ultralight, and Near Field Communication (NFC)-compatible cards. In the hardware design, two RFID modules have been optimized and integrated under the control of a single microcontroller. The system is capable of automatically detecting the card's frequency, switching to the appropriate protocol, and performing secure identity verification processes. Additionally, the device has been designed to be resistant to electromagnetic interference and capable of operating inside a metal enclosure, taking into account harsh environmental conditions. Thus, it can also exhibit reliable performance in areas such as industrial facilities, parking systems and dense metal environments. Thanks to this innovative approach, not only has compatibility with existing card infrastructures been achieved, but also an important step has been taken for long-lasting and secure access control systems.