Components:

R1=R2 = 10K       C1 = 22nF

R3 = 56K          C2 = 100nF 

R4 = 470K         IC = LM358

R5 = 68K          P1 = 470K potenziometer used as a variable resistor, 
                       used to set the gain. 
R6 = 6.8K         
                  P2 = 10K potenziometer used to set the threshold.
R7 = 1K           

Buzzer 12V

The values of R1 and R2 are calculated for + 5V input of IC1A (this is of course also the output of the sensor stages). For different values should be recalculated R1 and R2.
This stage has only one led as display and this is the most important and also drives the buzzer. If you want to have more leds you have to realize the 3 leds display stage.