The older DACTs format options were 3/1 Extended (Pulse) or BFSK. In this format, 0-9 and B-F are the only digits/characters it will send. With that in mind, most automation systems interpret an F9 (Fault Point 9) as a T9 (Trouble Point). An F9 report to the CS in 12 volt mode means a low battery. An F9 in 24 volt mode means the DC power input is less than 24.3 volts.