Smart home cameras (SHCs) offer convenience and security to users, but also cause greater privacy concerns than other sensors due to constant collection and processing of sensitive data. Moreover, privacy perceptions may differ between primary users and other users at home. To address these issues, we developed three physical cover prototypes for SHCs: Manual, Hybrid, and Automatic, based on design criteria of observability, understandability, and tangibility. With 90 SHC users, we ran an online survey using video vignettes of the prototypes. We evaluated how the physical covers alleviated privacy concerns by measuring perceived creepiness and trustworthiness. Our results show that the physical covers were well received, even though primary SHC users valued always-on surveillance. We advocate for the integration of physical covers into future SHC designs, emphasizing their potential to establish a shared understanding of surveillance status. Additionally, we provide design recommendations to support this proposition.

Cameras provide a vast amount of information at high rates and are part of many specialized or general-purpose devices. This versatility makes them suitable for many interaction scenarios, yet they are constrained by geometry and require objects to keep a minimum distance for focusing. We present the LensLeech, a soft silicone cylinder that can be placed directly on or above lenses. The clear body itself acts as a lens to focus a marker pattern from its surface into the camera it sits on. This allows us to detect rotation, translation, and deformation-based gestures such as pressing or squeezing the soft silicone. We discuss design requirements, describe fabrication processes, and report on the limitations of such on-lens widgets. To demonstrate the versatility of LensLeeches, we built prototypes to show application examples for wearable cameras, smartphones, and interchangeable-lens cameras, extending existing devices by providing both optical input and output for new functionality.

Smartphone-using pedestrians are often distracted, leading to frequent accidents of varying severity with a risk of both awkwardness and injury. We introduce HeadsUp, a mobile app designed to warn the user of imminent collisions with solid obstacles. HeadsUp runs on unmodified commodity smartphones without additional hardware and uses active ultrasound sensing based on the Doppler effect. We contribute an analysis of the ultrasound audio characteristics of six different smartphone models to verify the feasibility of our approach across vendors and device classes, and a description of two implementation variants of our signal processing pipeline. We evaluate our system both in a lab environment and under real-world conditions, and we conclude that HeadsUp can effectively work at a range of up to 3 meters, even though overall performance is heavily dependent on both the individual user and the environment characteristics.

From small tangibles to large tabletops, mirrors with complex geometries can be invaluable tools to reflect or form light for cameras and projectors. While many fabrication techniques are available for prototyping physical or electronic components, creating mirrors requires manual computation and industrial manufacturing equipment and is therefore considerably slower and more expensive. We propose a technique for fabricating mirror surfaces based on thermoplastics sheets with a laminated metallization layer and 3D-printed fixtures for bending or vacuum forming. Given our toolchain, a simulation of mirrors for cameras and projectors by rendering the CAD model is possible and allows to fabricate and evaluate design iterations quickly, making the process reasonably accessible for research. Finally, we show two prototypes for tangible interfaces based on our mirrors for projection and camera-based interaction, discussing advantages and limitations.

We present Seedmarkers, shape-independent topological markers that can be embedded in physical objects manufactured with common rapid-prototyping techniques. Many markers are optimized for technical performance while visual appearance or the feasibility of permanently merging marker and physical object is not considered. We give an overview of the aesthetic properties of a wide range of existing markers and conducted a short online survey to assess the perception of popular marker designs. Based on our findings we introduce our generation algorithm making use of weighted Voronoi diagrams for topological optimization. With our generator, Seedmarkers can be created from technical drawings during the design process to fill arbitrary shapes on any surface. Given dimensions and manufacturing constraints, different configurations for 3 or 6 degrees of freedom tracking are possible. We propose a set of application examples for shape-independent markers, including 3D printed tangibles, laser cut plates and functional markers on printed circuit boards.

We present TempoWatch, a wearable smartwatch-based interface designed to allow dance instructors to control music playback and tempo directly on their wrist via touch gestures using a circular watch display. Dance instructors have unique requirements with respect to music playback in their classes, in particular the ability to stay in position while controlling the playback, and to change speed via time-stretching. However, common stereo decks and mobile music player apps do not support these requirements well. We present the design and architecture of our system, and a qualitative evaluation performed with 9 semi-professional instructors in their own dance classes. Dance instructors were involved in this project from the very beginning to match the system and interface design to its prospective use cases. Results show that instructors are able to use TempoWatch productively after only a short learning phase.