This circuit, found in a 1958 magazine, is for reference only, since the components are not easy to find today. The transistors are germanium types and power supply is made by common cells.
This simple alarm was found in a 1982 documentation, but uses components that are still common,...
This fail-safe circuit was found in a 1967 Electronic Design. Transistors admit modern...
The sensor for this alarm is an LDR and it consists of an oscillator that goes into action when...