int ledpin=16;
int irpin =5;
int buzzerpin=4;

void setup()
{
Serial.begin(9600);
pinMode(ledpin, OUTPUT);    //voltage for LED
pinMode(irpin, INPUT);      // recieve data from ir sensor
pinMode(buzzerpin, OUTPUT); //Give value to buzzer

}

void loop()
{
digitalWrite(buzzerpin,0);   //buzzer should get value 0 by default. The case of no intrusion
int intensity=analogRead(A0);  // read the intensity of light in the room
analogWrite(ledpin,intensity);
if(digitalRead(irpin)==0){
digitalWrite(buzzerpin,1);   // Case of intrusion
delay(1000); // time  for which buzzer is ON
}

delay(500);

}