We found this circuit in the September 1971 Radio Electronics magazine. The SCR can be any of the 106 series and the buzzer can be replaced by a relay according to the supply voltage.
This interesting experimental and didactic configuration was found in a 1977 Radio Shack...
This is another of the circuits with the LM380 that we have in this section. We found it in an...
This commercial circuit, sold under the designation H531 in Japan in the 1960s, used three...