Access is provided to certain pulse oximetry systems utilizing a keyed sensor and a corresponding locked sensor port of a restricted access monitor. In such systems, the keyed sensor has a key comprising a memory element, and the monitor has a memory reader associated with the sensor port. The monitor is configured to function only when the key is in communications with the locked sensor port, and the memory reader is able to retrieve predetermined data from the memory element. The monitor is accessed by providing the key separate from the keyed sensor, integrating the key into an adapter cable, and connecting the adapter cable between the sensor port and an unkeyed sensor so that the monitor functions with the unkeyed sensor.