This circuit is for 12 V batteries but can be used with batteries of other voltages by changing the zener diode. The trigger point is adjusted by R1. The operating system accepts equivalents.
We found this circuit in the September 1971 Radio Electronics magazine. The SCR can be any of the...
This circuit uses unijunction transistors and drives a small speaker through an output...
The circuit presented was found in the Motorola Linear Databook of 1990. The power supply is...