Found in Electronics now from the 90s, this circuit uses a sensor from the time, which is difficult to find today. The circuit activates a sonalert-type buzzer.
This circuit is from a 1982 documentation. It can be modernized using LEDs in series with 470 ohms...
We found this circuit in a 1985 technical publication. The circuit uses PUTs to drive lamps....
This circuit appears with variations in other points of this section. This version is from...