Pairing of wireless devices, such as smartphones, suffers from a plethora of practical challenges if strong security guarantees via integrity codes are desired. Acoustic schemes are easy to deploy, but suffer from limited data rates and high sensitivity to environmental noise. Existing Wi-Fi-based methods, however, lack the necessary timing precision and signal flexibility to implement integrity codes on off-the-shelf devices. In this paper, we introduce Pair-Fi, a novel method that overcomes these limitations by leveraging integrity codes transmitted using software-defined radio (SDR)-like capabilities enabled through firmware modifications directly on smartphone-integrated Wi-Fi chips. Pair-Fi demonstrates both transmission and reception of raw IQ samples directly on commodity smartphone hardware, allowing for precise on-off keying modulation with timing resolution as low as 4 µs slots. By bypassing the constraints of conventional Wi-Fi frame timings, our approach significantly improves pairing speed, reliability, and resistance to interference. We validate Pair-Fi experimentally on recent smartphone models, such as the Google Pixel 7, showing robust performance in realistic environments. Our results indicate that SDR-enabled integrity code pairing via smartphone Wi-Fi chips provides a practical, secure, and efficient alternative to existing device pairing mechanisms, opening new avenues for secure and seamless device interactions in everyday scenarios.

Acoustic data transmission offers a compelling alternative to Bluetooth and NFC by leveraging the ubiquitous speakers and microphones in smartphones and IoT devices. However, most research in this field relies on simulations or limited on-device testing, which makes the real-world reliability of proposed schemes difficult to assess. We systematically reviewed 31 acoustic communication studies for commodity devices and found that none provided accessible source code. After contacting authors and re-implementing three promising schemes, we assembled a testbed of eight representative acoustic communication systems. Using over 11 000 smartphone transmissions in both realistic indoor environments and an anechoic chamber, we provide a systematic and repeatable methodology for evaluating the reliability and generalizability of these schemes under real-world conditions. Our results show that many existing schemes face challenges in practical usage, largely due to severe multipath propagation indoors and varying audio characteristics across device models. To support future research and foster more robust evaluations, we release our re-implementations alongside the first comprehensive dataset of real-world acoustic transmissions. Overall, our findings highlight the importance of rigorous on-device testing and underscore the need for robust design strategies to bridge the gap between simulation results and reliable IoT deployments.

Using smartphone apps during crises is well-established, proving critical for efficient crisis response. However, such apps become futile without an Internet connection, which is a common issue during crises. The ongoing 6G standardization explores the capability to provide local cellular connectivity for areas cut off from the Internet in crises. This paper introduces to the HCI community the concept of cellular island connectivity in isolated areas, promising a seamless transition from normal operation to island operation with local-only cellular connectivity. It presents findings from a survey (N = 857) among adult smartphone users from major German cities regarding their smartphone usage preferences in this model. Results show a shift in app demand, with users favoring general-purpose apps over dedicated crisis apps in specific scenarios. We prioritize smartphone services based on their criticality, distinguishing between apps essential for crisis response and those supporting routines. Our findings provide operators, developers, and authorities insights into making user-centric design decisions for implementing island-ready 6G communication.

Trustworthy digital communication requires the secure exchange of contact information, but current approaches lack usability and scalability for larger groups of users. We evaluate the usability of two secure contact exchange systems: the current state of the art, SafeSlinger, and our newly designed protocol, PairSonic, which extends trust from physical encounters to spontaneous online communication. Our lab study (N=45) demonstrates PairSonic's superior usability, automating the tedious verification tasks from previous approaches via an acoustic out-of-band channel. Although participants significantly preferred our system, minimizing user effort surprisingly decreased the perceived security for some users, who associated security with complexity. We discuss user perceptions of the different protocol components and identify remaining usability barriers for CSCW application scenarios.

Modern smartphones support FIDO2 passwordless authentication using either external security keys or internal biometric authentication, but it is unclear whether users appreciate and accept these new forms of web authentication for their own accounts. We present the first lab study (N=87) comparing platform and roaming authentication on smartphones, determining the practical strengths and weaknesses of FIDO2 as perceived by users in a mobile scenario. Most participants were willing to adopt passwordless authentication during our in-person user study, but closer analysis shows that participants prioritize usability, security, and availability differently depending on the account type. We identify remaining adoption barriers that prevent FIDO2 from succeeding password authentication, such as missing support for contemporary usage patterns, including account delegation and usage on multiple clients.

Smart home speakers have become a commodity item in many households and provide interesting research opportunities in areas like wireless communication and human-computer interaction. Commercial devices do not provide sufficient access for many research tasks. We present a modular smart home hub designed specifically for research purposes. The electronic and mechanical components are designed with reproducibility in mind and can be easily recombined for a project's needs. Additionally, we show applications of the hub in different scenarios.

Secure Device Pairing (SDP) relies on an out-of-band channel to authenticate devices. This requires a common hardware interface, which limits the use of existing SDP systems. We propose to use short-range acoustic communication for the initial pairing. Audio hardware is commonly available on existing off-the-shelf devices and can be accessed from user space without requiring firmware or hardware modifications.