It is good that the first transistor has a bypassed emitter resistor for good DC stability.
The second transistor is not needed.
Maybe an adjustment should be available to set the sensitivity.
Please connect a resistor in series with the base of the 3rd transistor to limit its base current.
The second transistor is not needed.
Maybe an adjustment should be available to set the sensitivity.
Please connect a resistor in series with the base of the 3rd transistor to limit its base current.