Unless you do design for something totally unambiguous like mobile phone OSs, you might has "what do you mean by mobile?" And the answer is, well, kind of a broad range of things, and not a very quick answer.

While other portable devices pre-date modern mobile telephony (both the Gameboy and the GPS network are earlier than GSM), mobile phones have evolved fastest, absorbed other technologies and form a useful core technology to consider all others. The evolution of mobile can be considered as:

1. Voice
2. Paging and Text
3. Pervasive network connectivity
4. General computing devices

If you consider a current mobile phone as a generally 4th era device instead, what you find is they are:

• Small - Small enough to carry with you all the time. Preferably in a pocket.
• Portable - Battery powered and otherwise independent of the world, so it doesn't have to be plugged in or attended to regularly.
• Connected - Wirelessly. Not attached to the wall or connected only when the user makes special effort. Whenever possible, connected in multiple ways, to both voice and data networks.
• Interactive - Inherently. Unlike a watch, or even most MP3 players, which are limited to display, playback and a small subset of interactions, more undirected actions can be taken, such as text entry and keyword search.

If we use this definition, then pretty much all mobile phones are included.

And some other devices in the "MID" (mobile internet device) range, such as the iPod Touch and the recent spate of mobile tablets. So, "mobile" is also:

• Things very like mobile phones, but without the mobile radio,
• and things very like mobile phones, but with different form factors.

But my device feels mobile also

But what if you are one of those folks who glues an iPad to down, to make it an ad hoc kiosk? It's no longer small, it's not portable anymore, so what is it?

Well, obviously it's a mobile device still. And if so, then the gut feeling is that so are GPS receivers, portable game systems, maybe even TV game systems. And then why not DVRs, and so on.

But certainly not TV video programming. And there are Windows tablets hardly bigger than many of the new iOS and Android tablets, which are clearly not particularly mobile-like, even if some of them are used on small screens, and in unusual environments.

So what makes some "mobile" and some just "not"? From a broader point of view, without as much focus on the hardware but the interaction and method of use, it seems to be:

• Contextually-aware
• Naturally-interactive
• Constrained interface

Take a Windows tablet PC, for example. It has pen input, but spottily implemented; text entry works well, but other controls are still in desktop-PC mode, so are hard to use. Many have GPS, cameras, audio input or even accelerometers. But they are not integrated with the OS, or the general user interaction; special software is required to use them, and in general the device doesn't know which way you are facing, where you are, or even react to whether it is day or night.

So, simply making a device small, connected and battery powered doesn't make it mobile because its not contextually-ware or naturally-interactive.

Consider the Wii, or X-Box Kinect instead. Though the display is not at all portable, they are at their core aware of user position, they change with the type of input being used, and the entire interface has been designed to support interaction via a game controller, or simply waving your arms at the screen. These meet the interactive criteria to be a "mobile" device.

The "constrained interface" bullet above might seem to be there just so we can arbitrarily say "mobile is small." However, it's as organically derived from user behaviors with these devices as the other bullets are. For example, if you put a real, full-size keyboard on a mobile device, the keyboard acts like a desktop computer, and suddenly all text input follows desktop computing patterns, not mobile patterns. The method by which the user interacts is the guiding principle in this defintion.

So, while this book does still focus on the classic answer, the mobile phone and especially the smartphone, similar interactions from kiosks to game stations to telematics, are also considered. In some cases, these may even be referred to in the pattern language.

So, which kind of devices are these?

In the end, a lot of devices have at least some of these attributes, and their design can be informed by mobile patterns. The ubiquity of mobiles also may mean that employing these as universal patterns is a good thing, as users may require less training when using interfaces to which they are accustomed.

A non-inclusive list of device and use categories that were considered during writing, or which are specifically mentioned in the book are:

• Mobile smartphones
• Mobile featurephones
• Mobile network access points (Aircards)
• MIDs
• Tablets
• eReaders
• Media players
• Image viewers and digital picture frames
• Portable game systems
• Remote controls
• Hand-held navigation devices
• Portable scanners
• Cameras and other capture devices
• Printers, scanners, copiers and mopiers (MFDs)
• Kiosks
• Wearable computers
• Telematics, and vehicle-mounted devices
• Industrial automation
• Portable surveying, measuring and metering equipment

Aside from the logical reasoning outlined above, we have worked on many of these categories of products -- at least a little -- and have had good results applying these principles to the design of interfaces for these devices.

So, what patterns are covered here?

Good question. And right now, it's purposefully muddled. We don't generally talk about hardware, except for labels and key functions and and keyboard layouts. Because those are pretty easy to change, and directly impact the on-screen interactions. Though we /could/ talk about how people with gloves, or dry fingers, or who just hate touchscreens should also have a scroll-and-select keys, at least as backup. But, that's pretty high level handset design, so not really worth fighting in a book like this.

So, the definition is pretty much on-screen, and things that directly impact the on-screen experience that are plausible to consider changing, for at least an operator/carrier to change, even if not everyone can.

If you have the ability to influence hardware design, then you can still get some hints from the patterns and principles contained here. We also, likewise, make lots of references to complying with the principles of the OS, as well as having principles that may conflict with any particular OS. So, if you design operating systems, then you have some other patterns and principles and guidelines to work off as well.