The touch screen, the fruit of recent IT development, is incorporated into many applications through a variety of touch screen smart devices. For smart phones, it provides convenient use of time and space for many people by replacing many desktop PC functions. Although this convenience has gained popularity among the public, the security is usually neglected. Inherent features are generalized, but the features also increase risk of exposing personal information. As a result, smart devices provide a variety of locking features to protect personal information. Although password and pattern lock features exhibit some degree of security, they are vulnerable to shoulder surfing or smudging. In this paper, vulnerable security points of smart devices are complemented and the locking system for security improvement (LSSI), in which intuitive user interface provides convenience, is proposed.