Punch in your secret key into this numeric matrix keypad. This keypad has 16 buttons, arranged in a telephone-line 4x4 grid. It's made of a thin, flexible membrane material with an adhesive backing (just remove the paper) so you can attach it to nearly anything. 

This keypad has 8 wires running from the bottom of the keypad, the wires connect in sequence from left to right and hook up to Arduino digital pin 2-9. You can get the Library from Arduino IDE, The following code below will allow you to test the keypad as each key is pressed, the corresponding character should appear on a separate line in IDE serial console.

Technical Details

• Weight: 7.5 grams
• Keypad dimensions: 69mm x 77mm x 1mm (2.75" x 3" x 0.035")
• Length of cable + connector: 83mm
• Connector: Dupont 7 pins, 0.1" (2.54mm) Pitch
• Mount Style: Self-Adherence
• Max. Circuit Rating: 35VDC, 100mA
• Insulation Spec.: 100M Ohm, 100V
• Dielectric Withstand: 250VRms (60Hz, 1min)
• Contact Bounce: <=5ms
• Life Expectancy: 1 million closures
• Operation Temperature: -20 to +40 °C
  
   

Arduino codes:
=============================================================================

#include // You need to include this library from your IDE

constbyteROWS=4;

constbyteCOLS=4;

charkeys[ROWS][COLS]={

{'1','2','3','A'},// Row 1

{'4','5','6','B'},// Row 2

{'7','8','9','C'},// Row 3

{'*','0','#','D'}  // Row 4

};

byterowPins[ROWS]={2,3,4,5};// Connect to Pin Row

pinouts

bytecolPins[COLS]={6,7,8,9};//connect to Pin Column

pinouts

Keypad keypad=Keypad(makeKeymap(keys),rowPins,

colPins,ROWS,COLS);

voidsetup(){

Serial.begin(9600);// Serial Console

}

voidloop(){

charkey=keypad.getKey();

if(key!=NO_KEY){

Serial.println(key);// Display to  Serial Console

}

}

=============================================================================

Tutorial:
1. Matrix Keypad Arduino Library