Mobile devices are generally used in public, where the user is surrounded by others not involved in the interaction. These devices often cause unnecessary disruption and distraction both for co-located people and the users themselves. Nevertheless, mobile devices do fulfill an important function, informing of important events and urgent communications, so they can't always be turned off in social settings. Interaction with mobile and wearable devices needs to be subtle, discreet, and unobtrusive; “intimate interfaces” are discreet interfaces that allow interaction with mobile devices through subtle gestures and peripheral cues in order to minimize disruption and gain social acceptance. Two novel examples of subtle intimate interfaces are available: an electromyogram (EMG) based, wearable input/output device that recognizes subtle, motionless gestures and provides haptic output; and a wearable peripheral display embedded in eyeglasses that delivers subtle, discreet, and unobtrusive visual cues.
A small wireless device embedded in an armband allows to interact with mobile devices in a subtle and unobtrusive way. The armband is meant to be worn under clothes and it detects discreet "motionless gestures", such as a short contractions of the upper arm. These gestures can be used to activate functions of a mobile phone or PDA, such as sending a pre-defined message or rejecting an incoming call. The armband provides haptic feedback through an embedded actuator. The device is, therefore, a self-contained input/output unit. Bluetooth wireless connectivity allows interfacing with standard mobile devices. The motionless gesture recognition is based on the electromyogram (EMG): an electrical signal generated by muscular activity. EMG is used to recognize activity related to very subtle or no movement at all (isometric activity). If a gesture is recognised the device transmits via Bluetooth an appropriate message containing the device ID and the parameters describing the gesture (if any). The armband is designed to potentially fit any user; it does not require calibration or training to the muscles of individual people. The EMG controller does not occupy the users' hands, and does not require them to operate it; hence it is "hands free.".