These circuits were found in Exar documentation from the 90s. The circuits use both a small speaker and a piezoelectric transducer. The integrated circuit is not common today.
This simple audio signal tracer or follower can be made with a BC548 instead of the original...
This circuit is from a 1982 publication. This is a way to stop 4017 at the end of a counting...
This circuit with analog indicator and diode bridge was found in Radio Electronics magazine from...