VIEWSONIC VS13394 - Manual (Page 21)

Tuning on the Device
Slide the Power switch to turn on the device
Slide the switch to turn on the device.
While the device is turned on. Slide the switch to enter
sleep mode or slide and hold the switch for 4 sec to
turn off the device.
Your eBook will also go to sleep by itself after a few
minutes if you are not using it.