The LTC1921, available in MSOP-8, plus three low cost resistors, provide a complete precision dual 㫈 V battery voltage and fuse monitoring solution for high reliability telecom equipment in less than 20 mm2. The three separate alarm outputs drive three optocouplers or green LEDs. Should either of the 㫈 V supplies have an undervoltage (㪾.5 V ۫ Vmax) or overvoltage (㫞 V ± 1.5 Vmax) failure condition, the LTC1921 turns off one or more of the LEDs/optos to indicate the fault to a diagnostic system. During an undervoltage condition, the LED/opto is held off until the supply recovers to 㫃 V (۪.5 Vmax). In addition, if the voltage across either fuse exceeds 2.5 V, indicating a blown fuse, the LTC1921 will turn off a third LED/opto. Because the 㫈 V supply is not always a benign environment, the LTC1921 has been design to withstand +100 V DC faults and 10 μs transients up to 𫐰 V.