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 was found in an Experimenters Handbook of the 1990s. The purpose of this circuit is to...
This source, from a 1982 documentation, uses a triac to control the power and voltage applied to...
This circuit was found in the September 1984 issue of Radio Electronics magazine. The circuit has...