MType: A Magnetic Field-based Typing System on the Hand for Around-Device Interaction

Smart wearable devices have become pervasive as they are portable and intelligent. The popular method to interact with it is touch-screen, which is error-prone and cumbersome due to its limited size. There are a few innovative works designing a virtual dial plate on the hand back, which need special-purpose sensors or microphones which may suffer from privacy leak. We propose MType, a system only employs sensors already built in the commercial-off-the-shelf (COTS) device with a magnetic ring to expand the interaction space between users and wearable devices. The core idea is to leverage the gravity sensor, linear accelerometer and magnetometer embedded in the standard smartwatch to detect gestures, capture input events and locate keystrokes on the opisthenar and palm. Besides, MType designs a runtime adaptation mechanism to handle the cold start problem and adapt to the variations over the time of usage. We implement MType on the COTS smartwatch and our extensive experiments in different scenarios show that the average accuracy of keystroke localization can reach 93% with a small size initial training set (3 samples for each key) at a low sampling rate (51Hz). Furthermore, when turning on the runtime adaptation mechanism and enlarging the training set, the accuracy can achieve 98%.