How can I add sounds to my logic probe?
Google "electronic buzzers" and choose one with high pitch and one with low pitch. Here is a page from Maplin that gives some ideas: -



Here's a tri-tone one (on maplin page also): -



There are plenty on the web and they work from DC so should easily interface to your circuit.

Here's a very small one that works from 1.5 volts to 5V: -