One of the reasons I like to go to campus to work, even in the summer, is that I’ve got two monitors in my office (like George), thanks to some timely grant money a couple of years back. This is excellent for copyediting, for working from digitized sources, and, really, for making my eyes feel less strained. It would be nice to have two monitors at home, but who has space for that?

If you have an iPad, there are apps, such as Air Display ($9.99) and DisplayPad ($2.99), that allow you to turn your iPad into a touchable second monitor. (See peril’s comments on this post about Air Display.) The apps basically work the same way: You install an app on your iPad, and then a utility on your computer, and from then on you can use the iPad as a display anytime you’re on the same wireless network as your home computer. You can set up either Air Display or DisplayPad as either a “second monitor” (i.e., more real estate!) or you can have your iPad mirror the display on your computer. (You can even, for example, watch Flash animations on your iPad via these apps. The horror!) Both Air Display and DisplayPad allow you to interact with apps, including via typing. Here, for example, is someone showing off Air Display:

Using the apps is almost an object lesson in the difference between touchscreen and mouse UI: it clarifies some of the stakes driving Apple’s decisions with iOS. Having said that, it can be remarkably useful to extend your computer in this way–especially if you’re using a desktop. (Let’s face it: if you have a MacBook Air, or some other ultralight notebook, portability isn’t as big of an issue!)

Both apps work via your wireless network, so there are no annoying cords, and the devices can be as far apart as your network reaches. By the same token, however, if your network is slow for any reason, then the performance of both apps will visibly degrade.

Air Display is only slightly more spendy than DisplayPad, but it also has more flexibility: it works on both OS X and Windows, and you can install it on any iOS device–handy for all those times you want to mirror your 27″ iMac monitor on an iPhone screen! By contrast, DisplayPad is Mac-only and iPad-only. If that is the only combination you want to use, though, in my experience DisplayPad is slightly smoother.

I use the app almost entirely for editing documents, for grading, and for typing in notes from various sources, and so the ability to control the Mac from the iPad is of less interest to me. You can see some of the challenges of using these apps for input by viewing these dueling videos of people running full-blown Photoshop on their iPad: first on DisplayPad, and second from Air Display. (Keep in mind, though, that the strength of the wifi network is the first predictor for how well the apps work.)

Do you use a mobile device as an additional monitor? What works for you? Let us know in comments!

Photo by Flickr user smemon87 / Creative Commons licensed