General Electric suggests this circuit in an 80's documentation. The circuit makes use of PUTs that are not common components today. Note the timing components that may change.
This freezer alarm was found in a 1980s American documentation. The circuit uses a reed switch and...
This circuit was found in a Popular Electronics documentation from the 90s. It is possible to switch...
This circuit was found in an old Radio Electronics, but can still be assembled as the components are...