This circuit is a pulse type oscillator with a very long OFF-time delay. In fact, the OFF-time delay is so long that someone has named this circuit the sleep machine. Probably because he fell asleep listening to the monotonous, hypnotizing, clicking sound.
Say, maybe we could call this the hypnosis machine. Well anyway, it is an interesting circuit. The basic circuit is a blocking oscillator as we discussed in detail in project Electronic Bird in Oscillator Section.
The added circuitry is the 9V Battery, Key and 470uF Capacitor. The change is in the source of base-bias. Instead of obtaining the bias from the 4.5V Battery through the 47K and 50K resistances, it is obtained from the 9V Battery or 470uF Capacitor charge.
Base-bias current requirements are so low that it takes a long time for the charge on the 470uF to leak down to near zero. Also the leakage of the 100uF and Transistor keep the circuit going slowly .... indefinitely. Pleasant dreams.