Energy management has become one of the great challenges in portable computing. This is the result of the increasing energy requirements of modern portable devices without a corresponding increase in battery technology. uSleep (pronounced micro-sleep) is an energy reduction technique for handheld devices that is most effective when the handheld is mostly idle, such as when the user is reading a document or looking at a web page. When idle, rather than using the processor's idle mode, uSleep tries to put the processor in sleep mode for short periods (less than one second) without affecting the user's experience. To enhance the perception that the system is on, an image is maintained on the display and activity is resumed as a result of external events such as touchscreen and button activity. We have implemented uSleep on a prototype pocket computer, where it has reduced energy consumption by up to 60%.