Fujitsu Point 1600 User Manual page 16

Your system may be configured to transition between these states automatically after
a period of inactivity to conserve battery power.
To determine the current system state, observe the Power LED. Table 1-1 on page 1-5
gives the different system states represented by the Power LED. (Note that if the
Power LED is off, the Off state is indicated.)
2-2 Using the Point 1600 Pen Tablet