Disclosed embodiments utilize a dual-frequency credential reader along with a dual-frequency access card that outputs two unique facility codes. A first facility code is associated with the legacy, low frequency credential transmission. A second facility code is associated with the secure, high frequency credential transmission. During the transition period, the new access readers are configured to read both low frequency, and high frequency credential data. The new access cards send out a first facility code at the first frequency, and a second facility code at the second frequency. In embodiments, the first facility code and second facility code of the new access cards are different than the facility code of the legacy cards. This allows users with new cards to use doorways at access points that still have legacy credential readers, simplifying the transition from a legacy access control system to a modern, secure access control system.