AirFlip: A Double Crossing In-Air Gesture using Boundary Surfaces of Hover Zone for Mobile Devices Hiroyuki Hakoda, Takuro Kuribara, Keigo Shima, Buntarou Shizuki, and Jiro Tanaka University of Tsukuba, Japan. {hakoda,kuribara,keigo,shizuki,jiro}@iplab.cs.tsukuba.ac.jp Abstract. Hover sensing capability provides richer interactions on mobile devices. For one such exploration, we show a quick double crossing in-air gesture for mobile devices, called AirFlip. In this gesture, users move their thumb into the hover zone from the side, and then move it out of the hover zone. Since this gesture does not conflict with any touch gestures that can be performed on mobile devices, it will serve as another gesture on mobile devices with touchscreens where only a limited input vocabulary is available. We implemented two applications based on AirFlip. In this paper, we show the results of a comparative user study that we conducted to identify the performance of AirFlip. We also discuss the characteristics of AirFlip on the basis of the results. Keywords: hover gesture, mobile, input method, in-air gesture. 1 INTRODUCTION Mobile devices with hover sensing capability have recently emerged such as ELUGA P P-03E and AQUOS PHONE ZETA SH-06E. This capability provides richer interactions on mobile devices. For example, it allows users to unlock a pattern lock without touching the touchscreen, accordingly enabling secure authentication because users do not leave their fingerprints on the touchscreen. Moreover, the capability can be used to detect a finger’s movement above the touchscreen, i.e., in-air gestures on mobile devices. However, few studies have explored in-air gestures in comparison with touch gestures on mobile devices. For one such exploration, we show a quick double crossing in-air gesture for mobile devices, called AirFlip, which uses side boundary surfaces of the hover zone. In this gesture, users move their thumb into the hover zone from the side, and then move it out of the hover zone (Fig. 1). Since this gesture does not conflict with any touch gestures that can be performed on mobile devices, it will serve as another gesture on mobile devices with touchscreens where only a limited input vocabulary is available. In this study, we conducted a comparative user study with only touch and Bezel Swipe [1] to identify the performance of AirFlip.