That is a great question, and there are a couple of ways to do that.
- Power the device off when not using it. See image one below.
- Set the sleep timer for your Xenvelabs devices. Instructions in listed below.
The easiest is to when you leave your desk for more than a few minutes, turn your Pen Tablet or Quick Keys off.
The image to the right shows the Power Off/On slider switch.
 Shows the location of the Pen Tablet On/Off power slider switch that is located in the upper-right corner of the tablet.
 Shows the On/Off power slider switch located at the bottom center of the Quick Keys.
Setting the Sleep Timer for your Pen Tablet and Quick Keys.
Setting the sleep timer if you have the Pen Tablet Bundle.
Open the Setting program and with both your Pen Tablet and Quick Keys connected and listed in the  Device window select Preferences.
Select Preferences 
 Then select dropdown the menu for Sleep Time For and select the  device you would like to set the sleep timer for.
 Select the amount of time you would like the device to be awaked if there is no interaction with it.
I set my devices to 30 minutes.