int buzz=13;
int trigpin=2;
int echopin=3;
long duration;
int distance;
void setup()
{
  pinMode(13,OUTPUT);
  pinMode(trigpin,OUTPUT);
  pinMode(echopin,INPUT);
  Serial.begin(9600);
}
void loop()
{
  digitalWrite(trigpin,LOW);
  delay(200);
  digitalWrite(trigpin,HIGH);
  delay(100);
  digitalWrite(trigpin,LOW);
  duration=pulseIn(echopin,HIGH);
  distance=(duration*0.034)/2;
  if(distance<=100)

  {
     digitalWrite(13,HIGH);
      Serial.println("person is entering into the room");
  }
  else
  {
     digitalWrite(13,LOW);
  }

}