Knocker: Vibroacoustic-based Object Recognition with Smartphones

While smartphones have enriched our lives with diverse applications and functionalities, the user experience still often involves manual cumbersome inputs. To purchase a bottle of water for instance, a user must locate an e-commerce app, type the keyword for a search, select the right item from the list, and finally place an order. This process could be greatly simplified if the smartphone identifies the object of interest and automatically executes the user preferred actions for the object. We present Knocker that identifies the object when a user simply knocks on an object with a smartphone. The basic principle of Knocker is leveraging a unique set of responses generated from the knock. Knocker takes a multimodal sensing approach that utilizes microphones, accelerometers, and gyroscopes to capture the knock responses, and exploits machine learning to accurately identify objects. We also present 15 applications enabled by Knocker that showcase the novel interaction method between users and objects. Knocker uses only the built-in smartphone sensors and thus is fully deployable without specialized hardware or tags on either the objects or the smartphone. Our experiments with 23 objects show that Knocker achieves an accuracy of 98% in a controlled lab and 83% in the wild.