This circuit can be used as an answering password system in a store, office, or other location. The circuit is from Intersil using components of the time. The circuit is from the 80's.
These days the unijunction transistor (UJT) is not common, but IF you have one you can mount this...
This circuit generates a pulse of approximately 1 second when the light incident on the sensor...
This bidirectional current sensing circuit was found in a 2005 Linear Technology application manual....