I agree with the above two posts, that were written when I was writing mine....
This is my humble opinion: It will not work
Le's examine it:
When the output is not shorted, there is some output voltage.
The green LED is on, D2 drives T2 base through R2, T2 collector is low, T1 base is low and so T1 does not conduct and the buzzer and the red LED are off.
Theoretically, if the output is shorted, T2 will not conduct (it's base will be low), so it's collector should go high and will drive T1 base.
The buzzer and the red LED will be ON.
The fact is that, if the ouput is shorted, the circuit will be powered by only 1 to 0.5 V (D1 direct drop) and so it will not operate (The supply voltage is not sufficient for the operation.
Maybe the circuit will work if it's supply (R1 and buzzer) is connected not to the ouptput voltage, but to the unregulated voltage feeding the regulator transistor or IC.
Best regards