Existing wearable hand gesture interaction devices are very bulky and cannot be worn in everyday life, because of the presence of a large visual feedback device. In particular, an eyeglass-type head-mounted display is very large for constant usage. To solve this problem, we propose Brainy Hand, which is a simple wearable device that adopts laser line, or more specifically, a mini-projector as a visual feedback device. Brainy Hand consists of a color camera, an earphone, and a laser line or mini-projector. This device uses a camera to detect 3D hand gestures. The earphone is used for receiving audio feedback. In this study, we introduce several user interfaces using Brainy Hand. (e.g., music player, phone).