Natural gas stove flameout alarm

The circuit shown is the second type of natural gas (gas)
stove flameout alarm . After the gas stove ignites and burns normally, close
the power switch S. Because the photoresistor RG is irradiated by the strong light of the flame,
its resistance value is very small, the transistors VT1 and VT2 are turned on, the relay
K is closed, its normal contact point II1 K is disconnected, and the music integrated block IC does not
make any sound. But once the gas stove is turned off, the light exposure of RG is greatly
weakened, and its resistance value increases, causing Vri and VTZ to cut off, the relay
K is released, the normally open contact K is closed, and
the power , IC works, and the speaker BL Sounds a music alarm to remind the owner
to close the gas valve in time.
    Except as noted in the circuit, the small relay uses JRX-13F with a working voltage of 12V. Transistor VT3 is 9014, which can
be replaced by 3DG4M, 3DG201, 3DG401 or 3DG8A, B, etc.
    Adjust the potentiometer RP to change the alarm sensitivity.