Security is prime concern in the day-to-day life. Everyone wants to be as much as secure as to be possible. An access control systems forms a vital link in a security chain. Door lock is use in doors to lock the door; it is a security strategy use for avoiding opening the door. Only rightful person can open the door. The Arduino controller based digital lock is an access control system that allows only authorized persons to access a restricted area. This system is best suitable for corporate offices, ATMs and home security. A Knock Based Security System (KBSS) system using a Piezo sensor and ARDUINO.