Many current smartphones need to be recharged every day despite only average usage. This problem is intensified when phones need to track their location on a continuous basis. We provide a yet unavailable platform for accurately measuring the energy consumption of different hardware/software solutions comparing up to three variants in a mobile setting. We show that the accuracy of our system is similar to a fixed, commercial system but is especially useful to evaluate and optimize technology and algorithms that require the phone to be used on the go.

Many interactions naturally extend across smart-phones and devices with larger screens. Indeed, data might be received on the mobile but more conveniently processed with an application on a larger device, or vice versa. Such interactions require spontaneous data transfer from a source location on one screen to a target location on the other device. We introduce a cross-device Drag-and-Drop technique to facilitate these interactions involving multiple touchscreen devices, with minimal effort for the user. The technique is a two-handed gesture, where one hand is used to suitably align the mobile phone with the larger screen, while the other is used to select and drag an object between devices and choose which application should receive the data.

We present the technical framework supporting a cross-device Drag-and-Drop technique designed to facilitate interactions involving multiple touchscreen devices. This technique supports users that need to transfer information received or produced on one device to another device which might be more suited to process it. Furthermore, it does not require any additional instrumentation. The technique is a two-handed gesture where one hand is used to suitably align the mobile phone with the larger screen, while the other is used to select and drag an object from one device to the other where it can be applied directly onto a target application. We describe the implementation of the framework that enables spontaneous data-transfer between a mobile device and a desktop computer.

Mobile devices can help to solve urban traffic problems by improving personal mobility and making transport, traveling, and commuting for individual users more flexible, sustainable, and rewarding. For that purpose, the tripzoom application combines mobility data and patterns from mobile sensing, a dynamic incentive system, and community feedback from social networks. This paper gives an overview of tripzoom, its features, and technical realization, and explains how users can take advantage of it to monitor, manage, and improve their mobility behavior.

Sharing social and contextual information via services like Facebook, Twitter or Foursquare has become extremely popular in the recent years. This paper introduces the novel MyState concept in which users can augment any kind of object with Near Field Communication (NFC) tags, can write any social or contextual information on those tags using their mobile phones and can publish this information on a social networking site just by touching such a tag with their phone. The distinct features of MyState are A) the possibility to augment any personal or public object with any contextual or social information, B) the possibility that everybody can touch those tags in order to post the related information to a social networking site, C) the speed and convenience to publish information by a simple touch as users don't have to look at the mobile phone screen, interact with mobile phone menus or write any text when touching an already deployed tag. The paper reports on two field studies which provide insights on where the participants placed the tags, how they used MyState and what type of information was shared. Here we observed that users typically shared identity, location, activity and time, but also feelings, social meanings and experiences. Furthermore we identified several distinct social usage patterns such as synchronizing activities, expressing moods, games and tracking shared items.

This paper documents MultiKit: a toolkit that supports the development of sophisticated user-interfaces for applications using Near Field Communication (NFC). The usage of the toolkit is exemplified using three implemented prototypes, each with significant differences. These differences highlight the complexities involved in producing such NFC applications, and the benefits of a toolkit that can adapt to varying interface types. As the toolkit is tailored to NFC technology, NFC-specific features are explored. These include switching between dynamic (e.g. projection) and static interfaces (e.g. posters), and interface generation from NFC tag descriptions.

Near Field Communication (NFC) is a technology for mobile, touch-based interaction with tagged objects that can serve as physical user interfaces (UI). Dynamic NFC-displays use a grid of NFC-tags as a physical UI and combine it with a projected application UI to enable direct interactions between mobile devices and large screens. In this paper, we explore the design of interaction techniques for dynamic NFC-displays beyond the common touch-select interaction with single tags and evaluate them with an NFC-pinboard prototype. A user study confirms the general preference for the simple touch-select, but also shows that other techniques can provide alternatives, e.g. to implement interactions for which users want to feel more in control.

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Mobile devices can take advantage of physical interaction with their environment and its objects to compensate their constrained input and output capabilities. For that purpose, dynamic NFC-displays combine the physical interaction with NFC-tagged user interfaces and the output capabilities of public displays. We have adopted this technology for the Whack-a-Mole game to show how it can improve the accessibility and usability of mobile games. This paper describes the design of the game and explores how physical interaction with dynamic NFC-displays can compensate the constraints of mobile games and enrich their gameplay.

This paper reports on a development framework, two prototypes, and a comparative study in the area of multi-tag Near-Field Communication (NFC) interaction. By combining NFC with static and dynamic displays, such as posters and projections, services are made more visible and allow users to interact with them easily by interacting directly with the display with their phone. In this paper, we explore such interactions, in particular, the combination of the phone display and large NFC displays. We also compare static displays and dynamic displays, and present a list of deciding factors for a particular deployment situation. We discuss one prototype for each display type and developed a corresponding framework which can be used to accelerate the development of such prototypes whilst supporting a high level of versatility. The findings of a controlled comparative study indicate, among other things, that all participants preferred the dynamic display, although the static display has advantages, e.g. with respect to privacy and portability.

NFC and RFID technologies have found their way into current mobile phones and research has presented a variety of applications using NFC/RFID tags for interaction between physical objects and mobile devices. Since this type of interaction is widely novel for most users, there is a considerable initial inhibition threshold for them. In order to get novice users started with this physical interaction and its applications, we have designed different ways to increase the learnability and guidance of such applications. Their effectiveness was evaluated in a qualitative and quantitative user study with 40 participants, who interacted with NFC-equipped posters in different ways. We report on the types of usage errors observed and show that future designs of NFC/RFID-based mobile applications should consider using a dedicated start-tag for interaction.

Exchanging data between a mobile phone and a computer such as a laptop is still a very cumbersome process. This paper presents two different techniques, touch & connect and touch & select, designed help to overcome this problem and facilitate and speed up spontaneous interactions between such devices. Using touch & connect, the user can physically touch a computer in order to pair a Bluetooth connection and initiate a file transfer between these two devices. Touch & select extends this concept in that users can select a specific object or location on the computer screen by simply touching it with the mobile phone. We report the implementation of these interaction techniques based on Near Field Communication (NFC) tags and present a formal, comparative study focusing on transferring images. The results provide clear evidence of the advantages of touch & connect and touch & select when compared with current Bluetooth-based implementations. Considering task completion time for uploading and downloading pictures, touch & select was 43% and touch & connect 31% faster than the conventional Bluetooth-based approach.

Uploading and downloading pictures between a mobile phone and a computer is still a very cumbersome process. Because of this, many users actually do not copy, move or backup their pictures onto another computer until the storage capacity of the mobile phone is reached. This paper presents the prototypes (and respective implementation details) of the touch & connect and touch & select interaction techniques. Both techniques allow the quick and easy exchange of pictures by touching the computer with the mobile device. The first interaction technique: touch & connect, allows the user to touch a computer with their mobile phone in order to establish a Bluetooth connection and initiate a file transfer between the two devices. The second interaction technique: touch & select, extends this concept and allows the selection of a specific picture or location on the computer screen by touching it with the mobile phone. The interaction techniques were implemented using Near Field Communication (NFC) tags attached to the computer and an NFC phone capable of reading those tags.

In their role as personal communication devices, mobile phones are a natural choice for sharing and communicating emotions. However, their functionalities are currently very limited in power to express affective messages. In this paper, we describe the design of a system that allows users to easily compose melodies and share them via mobile phones. We show that by using these melodies information about the current emotional state of the sender can be expressed and recognized synchronously by the receiver in a simple, quick, and unobtrusive way. Further, we reveal that self-composed melodies have a stronger impact than pre-composed or downloaded messages, similar to crafted pieces of art offered to a beloved person. We then present findings from a user study that assesses the implementation of a functional prototype and the adequacy of the system for emotional communication.

Wearable computing and smart clothing have attracted a lot of attention in the last years. For a variety of applications, it can be seen as potential future direction of mobile user interfaces. In this paper, we concentrate on usability and applicability issues concerned with capacitive touch input on clothing. To be able to perform user studies, we built a generic platform for attaching, e.g., capacitive sensors of different types. On top of that, several prototypes of wearable accessories and clothing and implemented various application scenarios. We report on two studies we undertook with these implementations with a user group randomly sampled at a shopping mall. We provide a significant set of guidelines and lessons learned that emerged from our experiences and those studies. Thus, developers of similar projects have to put major efforts into minimizing the delay between button activation and feedback and to make location and identification of controls and their function as simple and quick as possible. Issues that have to be treated in all designs include the requirement of one-handed interaction and that, even for minimal functionality, to find a general solution with regard to layout and button-to-function mapping is hardly possible. Additionally, in order to generate a satisfactory user experience good usability must be combined with aesthetical factors.

We present a platform to evaluate mobile phone applications that make use of an additional dimension for key presses. Using capacitive sensors on each key, merely touching buttons as well as the force of the press can be measured. A set of applications well known from current mobile phones has been extended with functionality exploiting those new possibilities. The results of a study undertaken with this prototype are presented and conclusions are drawn for the design and implementation of such applications.

The design of applications using mobile devices needs a different quality assessment than those known for desktop applications. Of the many aspects that have to be taken into account, one important criterion is the average time users need to complete a task. For interactions with the mouse, keyboard or touch screens, there exist models that predict interaction times like Fitts' law or the Keystroke-Level Model (KLM). This paper shows parallels to these models for advanced interactions with mobile phones targeted at pervasive services, including near field communication as well as built-in cameras and sensors. Applications can be evaluated with respect to user performance time without having a prototype running on the phone. To accomplish that, we extend the known KLM by identifying basic interaction elements for mobile phones and give estimates for expert user performance derived from several user tests.