The movement of a user's face, easily detected by a smartphone's front camera, is an underexploited input modality for mobile interactions. We introduce three sets of face-engaged interaction techniques for augmenting the traditional mobile inputs, which leverages the combination of the head movements with touch gestures and device motions, all sensed via the phone's built-in sensors. We systematically present the space of design considerations for mobile interactions using one or more of the three input modalities (i.e., touch, motion, and head). The additional affordances of the proposed techniques expand the mobile interaction vocabulary, and can facilitate unique usage scenarios such as one-hand or touch-free interaction. An initial evaluation was conducted and users had positive reactions to the new techniques, indicating the promise of an intuitive and convenient user experience.
@cite_28: We introduce Whack Gestures, an inexact and inattentive interaction technique. This approach seeks to provide a simple means to interact with devices with minimal attention from the user -- in particular, without the use of fine motor skills or detailed visual attention (requirements found in nearly all conventional interaction techniques). For mobile devices, this could enable interaction without "getting it out," grasping, or even glancing at the device. This class of techniques is suitable for a small number of simple but common interactions that could be carried out in an extremely lightweight fashion without disrupting other activities. With Whack Gestures, users can interact by striking a device with the open palm or heel of the hand. We briefly discuss the development and use of a preliminary version of this technique and show that implementations with high accuracy and a low false positive rate are feasible.
@cite_24: PhoneTouch is a novel technique for integration of mobile phones and interactive surfaces. The technique enables use of phones to select targets on the surface by direct touch, facilitating for instance pick&drop-style transfer of objects between phone and surface. The technique is based on separate detection of phone touch events by the surface, which determines location of the touch, and by the phone, which contributes device identity. The device-level observations are merged based on correlation in time. We describe a proof-of-concept implementation of the technique, using vision for touch detection on the surface (including discrimination of finger versus phone touch) and acceleration features for detection by the phone.
@cite_27: We present TimeTilt, a sensor-based technique that allows multiple windows switching on mobile devices, and which overcomes the limitations of mobile devices, i.e. their impoverished input bandwidth (often no keyboard, a small tactile screen and the drawbacks of one-handed interaction). TimeTilt, which is based on a lenticular metaphor, aims at both reducing the activation time when switching between views, and supporting a natural mapping between the gestures and the navigation. We draw a brief classification of sensor-based gestures that could be used in mobile conditions, and we present an experiment.
@cite_2: We describe sensing techniques motivated by unique aspects of human-computer interaction with handheld devices in mobile settings. Special features of mobile interaction include changing orientation and position, changing venues, the use of computing as auxiliary to ongoing, real-world activities like talking to a colleague, and the general intimacy of use for such devices. We introduce and integrate a set of sensors into a handheld device, and demonstrate several new functionalities engendered by the sensors, such as recording memos when the device is held like a cell phone, switching between portrait and landscape display modes by holding the device in the desired orientation, automatically powering up the device when the user picks it up the device to start using it, and scrolling the display using tilt. We present an informal experiment, initial usability testing results, and user reactions to these techniques.
@cite_15: 
@cite_17: Triggering shortcuts or actions on a mobile device often requires a long sequence of key presses. Because the functions of buttons are highly dependent on the current application's context, users are required to look at the display during interaction, even in many mobile situations when eyes-free interactions may be preferable. We present Virtual Shelves, a technique to trigger programmable shortcuts that leverages the user's spatial awareness and kinesthetic memory. With Virtual Shelves, the user triggers shortcuts by orienting a spatially-aware mobile device within the circular hemisphere in front of her. This space is segmented into definable and selectable regions along the phi and theta planes. We show that users can accurately point to 7 regions on the theta and 4 regions on the phi plane using only their kinesthetic memory. Building upon these results, we then evaluate a proof-of-concept prototype of the Virtual Shelves using a Nokia N93. The results show that Virtual Shelves is faster than the N93's native interface for common mobile phone tasks.
However, touches are not always convenient for a user. Examples include when one is wearing gloves or visually impaired, leading some researchers to leverage the device motions to design novel gestures for mobile phone interaction. Based on a user’s spatial awareness, Virtual Shelves supports triggering shortcuts mapped to a hemisphere space in front of the body @cite_17 ; however, external sensors for tracking the phone are required. Accelerometer and gyroscope are widely used internal sensors for detecting motion gestures, for instance: auto screen rotation based on a device’s orientation @cite_2 , rolling a phone on different axes to scroll or command @cite_15 , tapping the back of a device or jerking it @cite_27 , and whacking a phone with hard contact forces @cite_28 . Also, through coupling the accelerometer data and touch events on an interactive surface, PhoneTouch allows for direct target selection using the phone and a pick &drop style of data transferring @cite_24 .