In this paper, we explored the eyes-free interaction in personal space by allowing users tapping on their own arms with naturally provided haptic feedbacks upon the skins. The user study was conducted to know how users can precisely interact with and how users behaved to operate on their arm space. Through the user study, we have concluded that normal users can at most divide their arm space into 6 points between a wrist and an elbow with iterative practices. We also found that each user's divided pattern is unique comparing to the other users. We then concluded the design principles from the observations, and designed our interaction system, PUB (Point Upon Body), to demonstrate how interaction design can take benefits through those findings. Two scenarios, remote display control and mobile device control, are demonstrated through the invented UltraSonic device attached on a user's wrist to detect the user's tapped positions.