#include <Keypad.h>

const byte ROWS = 4; //four rows
const byte COLS = 4; //four columns
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};
String password = "";
byte rowPins[] = {5, 4, 3, 2}; //connect to the row pinouts of the keypad
byte colPins[] = {9, 8, 7, 6}; //connect to the column pinouts of the keypad

Keypad keypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );

void setup() {
  Serial.begin(9600);
  pinMode(11, OUTPUT);
  Serial.println("Input password");
}

void loop() {
  char key = keypad.getKey();
  if (key) {
    beep();
    if (key == 'D') {
      Serial.print("Your password : ");
      Serial.println(password);
      password = "";
    } else {
      password = password + String(key);
      Serial.println(key);
    }
  }
}
void beep() {
  tone(11,1000,50);
}