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Code :-

#include <Keypad.h>

char * password = “3690”; // To increase the passcode length change the numerical to the size after position

int position = 0;

const byte ROWS = 4; // 4 rows
const byte COLS = 4; // 4 columns

char keys[ROWS][COLS] =
{
{‘1′,’2′,’3′,’A’},
{‘4′,’5′,’6′,’B’},
{‘7′,’8′,’9′,’C’},
{‘*’,’0′,’#’,’D’}
}; //mapping of the keys done w.r.t to the grid keypad

byte rowPins[ROWS] = { 13, 12, 11, 10 }; //connection of rows pins to the Arduino
byte colPins[COLS] = { 9, 8, 7, 6 }; // connection of the columns pins to the Arduino

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

int Lock = 5; // Connecting the relay to the 5th pin

void setup()
{

pinMode(Lock, OUTPUT);
LockedPosition(true);
}

void loop()
{
char key = keypad.getKey();
if (key == ‘*’ || key == ‘A’) //OR operator used to lock the device back again
{
position = 0;
LockedPosition(true);
}
if (key == password[position])
{
position ++;
}
if (position == 4) // change this if you want to increase the password length
{
LockedPosition(false);
}
delay(100);
}
void LockedPosition(int locked)
{
if (locked)
{
digitalWrite(Lock, LOW);
}
else
{
digitalWrite(Lock, HIGH);
}
}

If you are getting a stray error then download the code from here

Circuit Diagram