The sensors in this circuit that triggers when the temperature goes out of a certain range are common diodes. The circuit is from the 1991 Reista Electronics Experimenter's Handbook.
In the figure we have a bistable multivibrator using an operational one. The circuit is from old...
This is another of the Star Trek red alert circuit that you can find on this site. We took this...
This circuit for testing zener diodes by lifting their curve on an oscilloscope was presented in...