Final answer:
The low air warning device is the SCBA component that warns when the system is reaching 20-25.
Step-by-step explanation:
The SCBA component that warns when the system is reaching 20-25 is the low air warning device. This device is designed to alert the user when their air supply is getting low and they need to exit the hazardous environment. It is important for the user to pay attention to this warning and exit the area to ensure their safety.