Flood alarm (CB7994E)

This circuit is from a 90s Popular Electronics. The transistors are of general use and the buzzer is a Sonalert type.

Gas and smoke detector (CB9810E)
This detector uses an unusual sensor today. The circuit is from an 80s documentation. Its...
Alarm and Immobilizer (CB24467E)
This circuit was found in the December 1976 issue of Radio Electronics magazine. The circuit...
Interface or Shield with Triac for Inductive Loads (CB13114E)
For inductive loads we have the configuration shown in the figure. Note that the opto-coupler...