As the old adage goes, when the only tool you have is a hammer, then every problem will look like a nail. Smartphones — and apps — have become so pervasive that they are becoming that proverbial hammer. I too often hear people say “let’s make an app for it!”, no matter what the problem is that they want to solve.

I like smartphones, I really do. They work in a variety of contexts, for a variety of users, and for a variety of tasks. They even do a pretty decent job in many of them. We use smartphones for much of our research at my workplace. The problems start only when you forget the limitations of touch interaction on smartphones and use them in a context that they are not suitable for.

With that in mind, I find the following points useful when thinking whether to use a smartphone or find a different solution.

What will the user be doing while she interacts with the smartphone?

Using the smartphone while pushing a shopping cart is different using it when free climbing. Using it when writing with the dominant hand is different from using it while talking.

How restricted are the user’s psycho-motor faculties while using the smartphone?

If the user’s hands are busy, she won’t be able to interact with the phone with both hands. If the user is talking on the phone and taking notes, she can’t tap on your interface at the same time. If the user is wearing gloves, she won’t feel where the side buttons are. Try this: Put on diver’s gloves or firefighter’s gloves and try to grab a phone — you’ll immediately understand what I mean. For extra challenge, imagine those gloves are wet, as when firefighting.

How does the user hold the phone usually?

Which areas of the touch screen are available for input? Which areas are available for output (i.e. are not covered by the user’s finger while trying to reach the input areas?) Will the user be able to reach all the corners with her thumb if she’s using the phone single-handed? What if she has a bigger phone? Will the user unadvertently touch anywhere else on the screen?

…when trying to reach the upper part of the screen while holding the phone in my right hand, the base of my thumb sometimes touches the lower part of the screen, leading to undesired results. 1

How will the smartphone’s operating system interfere with the task?

For extra challenge: what will happen if the OS interferes unexpectedly in a critical situation?

…when waking up and lying in bed, my head is turned sideways. If I hold the phone sideways, however, it switches to horizontal mode, not allowing me to read. I have to hold the phone vertically, which, in that position, is unnatural to me. 2

Ok, I get this is important — show me the numbers!

I’ve been looking for a while for data to answer at least some of these questions, and was happy to discover a dataset by Steven Hoober. For example:

  • 49% of users use their smartphone one-handed
  • 36% cradle the phone in one hand and interact with it with the other hand
  • 15% keep the phone with both hands.

Of those that use the phone with only one hand, 67% use their right thumb on the screen (i.e. phone is kept on right hand). The rest, 33%, keep the phone in their left hand. Notice that this is much higher than the global average of 10-12%. For interface design, this means you will have a considerable number of users who are right-handed but are using their phones with their left, i.e. do not have as good control of their thumb as you will expect.

The original article has the full details of Steven Hoober’s study and is very well written, well illustrated, and a very useful read. The raw data are here (Google Doc).

As parting thought, here’s another smartphone interaction concept: Unifone 3

  1. From John M. Bueker in a comment
  2. From John M. Bueker in a comment
  3. See the paper