Code lock is used for access control. User has to enter 1 to 4 digit code (in free version) to unlock the door or several doors if needed. Code is entered via button keypad matrix. Optionally there can be LCD module connected.
For free light version author provides project schematic and hex file. If you see this project valuable you may purchase preprogrammed Attiny2313 with more codes and professionally made PCB. Check out the site for more interesting information including programmer, GSM alarm. Some of pages are in Slovakian language.