This circuit was found in a Popular Electronics from the 90's. The transistors are general-purpose types and the loaded load depends on the voltage and must have a maximum current of 100 mA.
If the input voltage falls below 12 V the LED glows up. Other voltages can be monitored by...
ON Semconductor FFSP0665B 650V 6A SiC Schottky Diodes Available through Mouser Electronics, these...
This adjustable circuit from 0 to 200 nA was found in a 90's EDN. The components can still be...