cal waves through the human brain will be used. Humans have five direct input channels-sight, hearing, smell, feel, and taste-and two output communications channels-speech and limb movement. Machines, on the other hand, can have a large number of input and output channels, but today they are limited by the range of human capabilities. The future promises to allow the use of indirect human communications channels, including thoughts, emotions, brain waves, and gaze tracking. Affective Computing Affective computing, in essence, involves building emotions into computers. It gives computers the capability of recording human responses and identifying behavior patterns. Wearable computers are sensors embedded in clothing that register bio- logical and physiological parameters and communicate them, if appropriate. Such biometrics opens the door to security applications based on the unique properties of the physical attributes of a human, including voice, fingerprints, hand geometry, the shape of the face, or the structure of the iris. One goal of affective computing is to build computer systems that can sense users' emotional states. Imagine a computer that can detect that you are frustrated and pause to help you overcome your problem. One approach to achieving this goal would be through affective wearable computing-wearing small but powerful computers in your clothing that use noninvasive biosensors to sense biophysiolog- ical changes that reflect changes in emotional state. An affective jewelry project is an attempt to create low-cost biosensors that are comfortable and aesthetically acceptable and that fit into the existing kinds of clothing that people wear. Skin conductivity sensors have been integrated into rings and shoes, and an earring has even been made out of a blood volume pressure sensor. A pair of galvanic skin response shoes may not be the height of fashion yet, but they could help you monitor your heart rate or reduce your blood pressure. Another possibility in the realm of affective computing is express