#define TRIGPin 3
#define ECHOPin 2
#define SWPin 4
#define BUZZPin 5

#define TONE_USE_INT
#define TONE_PITCH 440

#include <LiquidCrystal_I2C.h>
#include <TonePitch.h>

LiquidCrystal_I2C lcd(0x27, 20, 4);

void setup() {
  pinMode(BUZZPin, OUTPUT);
  pinMode(TRIGPin, OUTPUT);
  pinMode(ECHOPin, INPUT);
  pinMode(SWPin, INPUT_PULLUP);

  lcd.init();
  lcd.backlight();

  Serial.begin(9600);
}

void clearLCD(int line=4) {
  if (line == 4) {
    for (int i = 0; i < 3; i++) {
      lcd.setCursor(0, i);
      lcd.print("                    ");
    }
  }

  else { lcd.setCursor(0, line); lcd.print("                    "); }
}

int checkOnline() {
  clearLCD(0);

  if (digitalRead(SWPin) == 1) { lcd.setCursor(0, 0); lcd.print("System is On"); return 1; }
  else { lcd.setCursor(0, 0); lcd.print("System is Off"); return 0; }
}

void loop() {
  if (checkOnline()) {
    digitalWrite(TRIGPin, HIGH);
    delayMicroseconds(10);
    digitalWrite(TRIGPin, LOW);

    int duration = pulseIn(ECHOPin, HIGH);

    while ((duration / 58) <= 4) {
      if (!checkOnline()) break;

      lcd.setCursor(0, 2);
      lcd.print(" !Intruder Caught! ");

      tone(BUZZPin, NOTE_A3, 500);
      delay(400);
      tone(BUZZPin, NOTE_B8, 500);
      delay(400);
    }

    tone(BUZZPin, NOTE_C0, 500);
    clearLCD(2);
  }

  delay(100);
}