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.
I found this circuit in a Popular Electronics from November 1993. It allows to use a 12 V x 1 A...
This 1970s RCA circuit can be triggered by light or dark, depending on how the LDR is connected....
June 2017 - The new ROHM Low Dropout Voltage Regulators (LDOs) for 3.3 V or 5.0 V high accuracy...