Smartwatches gained popularity in the mainstream, making them into today’s de-facto wearables. Despite advancements in sensing, haptics on smartwatches is still restricted to tactile feedback (e.g., vibration). Most smartwatch-sized actuators cannot render strong force-feedback. Simultaneously, electrical muscle stimulation (EMS) promises compact force-feedback but, to actuate fingers requires users to wear many electrodes on their forearms. While forearm electrodes provide good accuracy, they detract EMS from being a practical force-feedback interface. To address this, we propose moving the electrodes to the wrist—conveniently packing them in the backside of a smartwatch. In our first study, we found that by cross-sectionally stimulating the wrist in 1,728 trials, we can actuate thumb extension, index extension & flexion, middle flexion, pinky flexion, and wrist flexion. Following, we engineered a compact EMS that integrates directly into a smartwatch’s wristband (with a custom stimulator, electrodes, demultiplexers, and communication). In our second study, we found that participants could calibrate our device by themselves <?TeX $\sim 50 \%$?> Math 1 faster than with conventional EMS. Furthermore, all participants preferred the experience of this device, especially for its social acceptability & practicality. We believe that our approach opens new applications for smartwatch-based interactions, such as haptic assistance during everyday tasks.

Vertical force-feedback is extremely rare in mainstream interactive experiences. This happens because existing haptic devices capable of sufficiently strong forces that would modify a user's jump require grounding (e.g., motion platforms or pulleys) or cumbersome actuators (e.g., large propellers attached or held by the user). To enable interactive experiences to feature jump-based haptics without sacrificing wearability, we propose JumpMod, an untethered backpack that modifies one's sense of jumping. JumpMod achieves this by moving a weight up/down along the user's back, which modifies perceived jump momentum—creating accelerated & decelerated jump sensations. In our second study, we empirically found that our device can render five effects: jump higher, land harder/softer, pulled higher/lower. Based on these, we designed four jumping experiences for VR & sports. Finally, in our third study, we found that participants preferred wearing our device in an interactive context, such as one of our jump-based VR applications.

We present a technique to render tactile feedback to the palmar side of the hand while keeping it unobstructed and, thus, preserving manual dexterity during interactions with physical objects. We implement this by applying electro-tactile stimulation only to the back of the hand and to the wrist. In our approach, there are no electrodes on the palmar side, yet that is where tactile sensations are felt. While we place electrodes outside the user's palm, we do so in strategic locations that conduct the electrical currents to the median/ulnar nerves, causing tactile sensations on the palmar side of the hand. In our user studies, we demonstrated that our approach renders tactile sensations to 11 different locations on the palmar side while keeping users’ palms free for dexterous manipulations. Our approach enables new applications such as tactile notifications during dexterous activities or VR experiences that rely heavily on physical props.