Although the Kindle Fire has an HDMI socket, it is for output only so you can't simply plug it in and use it as a second monitor on your computer desktop to extend the display. Instead you can install one of two Fire applications, both of which connect to a related piece of software on your computer and allow you to extend the display by sending the information through Wi-Fi. Both applications have a purchase fee as of July 2013. Note that it isn't possible to use other Kindle devices as a second screen without advanced technical skills and the risk of invalidating your warranty.
iDisplay
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Step 1
Download and install the iDisplay app from the Android store on the Amazon website (see Resources). Download and install the associated software from the Shape Services website or website (see Resources).
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Step 2
Open and run the software on your PC or Mac. Open the iDisplay app on the Kindle Fire, making sure your computer and Kindle are on the same local network. Select your computer from the list of options in the app.
Step 3
Drag a window off your main computer screen -- it will now appear on your Kindle Fire screen as if it were a second monitor attached to your computer. You can move your mouse off your main screen and onto the Fire screen and tap and drag items directly on the Fire screen itself.
Air Display
Step 1
Download and install the AirDisplay app from the Android store on the Amazon website (see Resources). Download and install the associated software from the Avatron website (see Resources).
Step 2
Open and run the software on your PC or Mac. Open the Air Display app on the Kindle Fire, making sure your computer and Kindle are on the same local network. Select your computer from the list of options in the app.
Step 3
Drag a window off your main computer screen; you'll only be able to do this in one direction, though you can change this in your computer's operating system to take account of where you have placed your Kindle Fire in relation to the computer monitor. The window will now appear on your Kindle Fire screen as if it were a second monitor attached to your computer. You can move your mouse off your main screen and onto the Fire's screen. You can also tap and drag items directly on the Fire screen itself. With some computer applications you can use finger gestures for tasks such as drawing in a paint applications.
Step 4
Rotate your Kindle screen if you want to change screen orientation. With Air Display, the content will automatically reflow to the new orientation.