Arduino PIR ,MONTION Sensor circuit

code :

       int calibrationTime = 30;

//the time when the sensor outputs a low impuls
e
long unsigned int lowIn;
//the amount of milliseconds the sensor has to be low
//before we assume all motion has stopped
long unsigned int pause = 5000;
boolean lockLow = true;
boolean takeLowTime;
int pirPin = 12;    //the digital pin connected to the PIR sensor's output
int ledPin = 13;
////
//SETUP
void setup(){
Serial.begin(9600);
pinMode(pirPin, INPUT);
pinMode(ledPin, OUTPUT);
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);
}
//LOOP
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;       
}
//if the sensor is low for more than the given pause,
//we assume that no more motion is going to happen
if(!lockLow && millis() - lowIn > pause){
//makes sure this block of code is only executed again after
//a new motion sequence has been detected
lockLow = true;
Serial.print("motion ended at ");      //output
Serial.print((millis() - pause)/1000);
Serial.println(" sec");
delay(50);
}
} 

}