circuit elements purpose

Hi, maybe anyone can answer me what's the purpose of these elements in circuit on page 7:

• 3 transistors
• 2 capacitors
• zener diode and 1N418 diode

**broken link removed**

I would be glad if anyone can help me (sorry for such a lame questions, Im just a beginner in electronics)

Transistor T1 is the transistor that is the active gain device to produce oscillation in the coils L1, L2.

Transistor T2 seems to be part of a detector circuit using 1N4148 diode to detect oscillation level and produce a increasing bias to turn on the buzzer BUZ1.

Transistor T3 is used as a switch. When it gets turned on, it completes the buzzer circuit. LED1 is in series with the buzzer. It will light up when T3 conducts.

Zener diode ZD1 is a shunt voltage regulator. It condusts to drop the 9V battery voltage to 3.9V by losing the remainder in R2. The 3.9V is then the suitable voltage to be used by the T1 and T2 circuits. T3 is different. It needs the whole 9V to work the buzzer.

Capacitor C1 is part of the oscillator circuit. It helps set the frequency. Capacitor C2 is a smoothing capacitor, to remove the AC component from the DC voltage being used to turn on T3.

Thank you, you helped me so much