This circuit was found in a 1980s documentation. The diodes may be general purpose diodes such as 1N34 or 1N60 and the indicator may be the lowest current range of a multimeter.
In the figure we have another application for the LT3518 integrated circuit from Linear Technology...
This alarm with sensors in series and parallel was found in the 1995 Encyclopedia of Electronic...
Using only one integrated circuit this control was found in an 80's Electronic Engineering. The circuit...