Electronic Key

I´M TRYING TO MAKE AN ELECTRONIC KEY WHICH EACH USER INSERTS A DIFFERENT PERSONAL NUMBER (PIN) AND IT CAN BE CONTROLLED THE ONE´S WHO USES IT AND THE ONE´S WHO DOESN´T.
FOR THAT, IT´LL BE CONNECTED TO A PERSONAL COMPUTER BY THE SERIAL PORT WHERE THE DATABASE WILL BE IN, WITH THE VALID PERSONAL NUMBERS WHICH WILL ACTIVATE THE RELAY.
AT THE SAME TIME THE USERS WHO GAIN ACCESS MUST BE REGISTERED TOGETHER WITH THE DATE AND THE ACCESS TIME.
HOW MAY I SEND BY THE SERIAL PORT FOUR DIGITS COMBINATIONS FROM A MATRIX KEYBOARD 4x4?
PLEASE, CAN YOU HELP ME?