This alarm circuit with NC sensors in series was taken from an article in Radio Electronics magazine from May 1971. The SCR can be any of the 106 series.
This circuit is from a 1965 General Electric Hobby manual. The circuit uses only passive...
We found this circuit in a 1967 RCA SCR manual. The circuit uses components from the era. The...
Found in American documentation from the 1970s, this circuit can be designed based on a modern SCR,...