Need help with arduino coding for project

/* Knock Sensor

 * ----------------

 *

 * Program using a Piezo element as if it was a knock sensor.

 *

 * We have to basically listen to an analog pin and detect 

 * if the signal goes over a certain threshold. It writes

 * "knock" to the serial port if the Threshold is crossed,

 * and toggles the LED on pin 13.

 *

 * (cleft) 2005 D. Cuartielles for K3

 * edited by Scott Fitzgerald 14 April 2013

 */



int ledPin = 13;

int knockSensor = 0;               

byte val = 0;

int statePin = LOW;

int THRESHOLD = 100;



void setup() {

 pinMode(ledPin, OUTPUT); 

 Serial.begin(9600);

}



void loop() {

  val = analogRead(knockSensor);     

  if (val >= THRESHOLD) {

    statePin = !statePin;

    digitalWrite(ledPin, statePin);

    Serial.println("Knock!");



  }

  delay(100);  // we have to make a delay to avoid overloading the serial port

}

int calibrationTime = 30;        

long unsigned int lowIn;         
long unsigned int pause = 5000;  

boolean lockLow = true;
boolean takeLowTime;  

int pirPin = 3;    //the digital pin connected to the PIR sensor's output

void setup(){
  Serial.begin(9600);
  pinMode(pirPin, INPUT);
  digitalWrite(pirPin, LOW);

  //give the sensor some time to calibrate
  Serial.print("calibrating sensor ");
    for(int i = 0; i < calibrationTime; i++){
      Serial.print(".");
      delay(1000);
      }
    Serial.println(" done");
    Serial.println("SENSOR ACTIVE");
    delay(50);
  }
void loop(){

     if(digitalRead(pirPin) == HIGH){
       digitalWrite(ledPin, HIGH);   //the led visualizes the sensors output pin state
       if(lockLow){  
         lockLow = false;            
         Serial.println("---");
         Serial.print("motion detected at ");
         Serial.print(millis()/1000);
         Serial.println(" sec"); 
         delay(50);
         }         
         takeLowTime = true;
       }

     if(digitalRead(pirPin) == LOW){       
       digitalWrite(ledPin, LOW);  //the led visualizes the sensors output pin state

       if(takeLowTime){
        lowIn = millis();          //save the time of the transition from high to LOW
        takeLowTime = false;       //make sure this is only done at the start of a LOW phase
        }
       if(!lockLow && millis() - lowIn > pause){  
           lockLow = true;                        
           Serial.print("motion ended at ");      //output
           Serial.print((millis() - pause)/1000);
           Serial.println(" sec");
           delay(50);
           }
       }
  }

#define trigPin 13
#define echoPin 12
int buzzer = 6;

void setup()
{ pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
pinMode(buzzer,OUTPUT);
}

void loop()
{ long duration, distance;
digitalWrite(trigPin, LOW); 
delayMicroseconds(2); 
digitalWrite(trigPin, HIGH);
delayMicroseconds(10); 
digitalWrite(trigPin, LOW);

duration = pulseIn(echoPin, HIGH);
distance = (duration/2) / 29.1;

if (distance < 100) // Checking the distance, you can change the value
{ 
// When the the distance below 100cm
digitalWrite(buzzer,HIGH);
} else
{
// when greater than 100cm
digitalWrite(buzzer,LOW); 
} delay(500);
}