This is a schematic of a type of audio oscillator known as a twin “T” phase shift oscillator. It gets its name from the phase shift network made up of R3, R4 and C3 plus C1, C2 and R2 which shifts the phase of the signal fed back from the collector to the base by 180 degrees to make the oscillator oscillate.
You will notice that the emitter of Q1 is not connected. Bringing this connection to ground will turn on the oscillator or “key it” as it’s called. You could connect this to a telegraph key and make a code practice oscillator, or you could connect this to one of the collectors on the LED flasher.
Then when that LED comes on the oscillator will start. This will cause it to ‘beep’ when the led flashes.Now we need to be able to connect a speaker to it so we can hear the tone. To do this we need an audio amplifier to have enough power to drive a small speaker.Near the bottom of the drawing you will see the output which will connect to the audio amplifier.