Two displays for a single computer give you more space to spread out your documents, spreadsheets and web browsers. If you already own an Android tablet, why not? It's cheaper than buying an extra monitor and only requires a few app downloads.
There are a few apps that let you do this, but for this guide, I've chosen iDisplay since it it has options for multiple platforms.
What you need
A Wi-Fi connection
An Android tablet running Android 2.01 or newer, or an
7 or later
A PC running Windows XP, Vista or 7 (32-bit or 64-bit), or a Mac computer running,
Mavericks 10.9 or newer
1. Install iDisplay on your tablet
You can easily find the app in the Google Play Store ($5.99) or Apple App Store ($19.99). No, the apps aren't free, but they're cheaper than a new monitor. Once installed and opened, you'll see one option -- connect via USB. (I found this method worked inconsistently, if ever.) To connect via Wi-Fi instead, you have to download iDisplay for your PC or Mac (see step 2), before this option appears. When connecting via Wi-Fi, you have to make sure both tablet and computer are connected to the same network.
2. Install iDisplay on your computer
iDisplay is available for Windows and Mac and both work the same way. Once downloaded, you can install the software in just a few clicks. The installation requires you to reboot the machine.
3. Pairing with the tablet
Once rebooted, click on the icon to start up iDisplay. If using a PC, a Windows Firewall exception request may appear. After allowing the exception -- and making sure both devices are connected to the same wireless network -- you can make a connection between the tablet and the computer.
When you attempt to connect, a dialog box pops up and you can either allow iDisplay to connect to the tablet once only, always allow it to connect, or deny it. If you plan on using it often, select "always allow."
On the tablet, a list of devices which the tablet can pair with will show up on the app. Tapping on the device you want to pair with will then connect the tablet to the computer.
After connecting, you can adjust the display size. In the settings page (the cog icon in the top-right corner of the connection page in the iDisplay app on your tablet), you can choose from four different resolutions. A higher resolution works better on the small tablet. (Choosing a smaller resolution results in the tablet displaying windows with huge text and overstretched pictures.)
On your computer, you can also right-click on the system tray icon to quit iDisplay or bring up the "Display Arrangement" option, which allows you to select where you want the tablet to be relative to the main display.
Performance of the tablet display can vary depending on the speed of your Wi-Fi connection (a faster network will increase the responsiveness of the display), as well as the tablet's processor speeds and graphics capabilities.