Hand-held devices are rapidly becoming a common technology at work, school, and play. Even though battery technology is improving continuously and processors and displays are rapidly improving in terms of power consumption, battery life is an issue that will have a marked inuence on how hand-held computers can be used. Energy consumption can be reduced by the efficient usage of the three power states: Run, Idle and Sleep. _Sleep is an energy reduction technique for handheld devices which is different from the common implementation of the system sleep state, where the device appears as if it was turned o_. A study of this new technique has been made.