#include <LiquidCrystal.h>
int trigPin=5;
int echoPin=18;
const int buzzer=4;

long duration;
int distance;

void setup() {
  Serial.begin(9600);
  pinMode(echoPin, INPUT);
  pinMode(trigPin, OUTPUT);
   pinMode(buzzer, OUTPUT);
}

void loop() 
{
  digitalWrite(trigPin, LOW);
  delay(2);
  if(digitalRead((trigPin, HIGH)){
    digitalWrite(buzzer, HIGH);

  }

  delay(10);
  digitalWrite(trigPin, LOW);

  duration=pulseIn(echoPin,HIGH);
  distance=duration*0.0034/2;
  Serial.println("someone entered in room");
  delay(1000);
}