MagPie: Extending a Smartphone's Interaction Space via a Customizable Magnetic Back-of-Device Input Accessory

초록

Back-of-Device (BoD) interfaces have emerged as a promising solution to free up screen real estate in smartphones by offloading interactions from the display to the back, thereby reducing reliance on on-screen interfaces. However, existing BoD solutions face limitations, such as requiring specialized hardware, consuming excessive power, or offering limited input vocabularies. We introduce MagPie, a novel BoD interface that leverages the magnetic phenomenon induced by MagSafe, part of the wireless charging standard. Users can seamlessly attach MagPie to MagSafe-enabled smartphones and interact using tangible, modular interfaces that generate unique magnetic signals upon activation. MagPie then detects these signals and recognizes the input through magnetic sensing. Our experiments with real-world users demonstrate that i) MagPie achieves high performance in accuracy, usability, deployability, responsiveness, and robustness across diverse environments, and ii) its tangible, intuitive, and customizable design opens up possibilities for a whole new class of smartphone interaction scenarios. © 2025 Copyright held by the owner/author(s).

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