Designing a better cell phone user interface
Given that the cell phones on the market seem to be so often badly designed - at least in terms of usability - it seems that the industry could use some sort of design reference. Cell phones have been on the mass-market for rather a while. Surely by now someone would have taken a stab at writing up some sort of guidelines, or offered some sort of reference design?
Went searching and - oddly enough - did not come up with much.
Seems that most of the guidelines are focused on folks with disabilities. To be brutally honest, free-market companies care very little about the disabled as they represent only a very small portion of the market. On the other hand, there does not seem to be focus on usability for mainstream consumers. Maybe I did not look in the right places. On the other hand, since the end result - the devices on the market - is so poor, we have to assume that effectively no one else is able to find relevant information.
From personal experience I can take a rough first cut at guidelines:
- Screen contrast - for color screens use Colour Contrast Check and the referenced material as a starting point.
- Screen contrast - for monochrome screens beware lack of contrast in mid-level light conditions. I find the screen on my Kyocera 6035 easy to read on full sunlight and full dark (with backlight), but relatively hard to read in a room with open windows and daylight outside.
- Screen element sizing - for fonts you should be looking at the same guidelines as computer screens. Anything below 12pt at 72dpi should be considered dubious.
- On screen elements - where possible you want to use a few common well-recognized icons for common features (battery-full, signal-strength-bars, mail-envelope, ring-speaker). New unrecognizable icons should be considered dubious. The end-test is to ask users what icons mean. If they do not know (and many do not), consider that a problem in your design.
- Screen size - consider that you want to present the full phone number (or at least last seven digits) in an upsized/bold font across the width of the display. By my measure this suggests a minimum display width of somewhere around 30-40mm.
- Button sizing - you want the size of a key to be about the size of the fingertip pressing the button. Wet your finger, press it against a surface and measure the resulting impression. I get about 10mm tall and 12mm wide. If you only want to market to children or small women, you can use smaller buttons. Note that for the usual three-across keypad this suggests about 36mm minimum width.
- Button placement - the user should be able to identify and press a unique button by both look and feel. Trying out the phones offered in the Verison store recently, I found myself checking the screen to verify the button pressed (a lot). If you watch other folks using their cell phones, you will see a lot of double-checking the screen to verify the key pressed.
I am sure with thought, working examples (and counter-examples), additional guidelines would be easy to come by. Note that the minimum usable widths given above for the screen and keypad both work out to about the same (a big hint perhaps?).
Consumer Reports sent out another survery lately, asking which areas we thought they should focus their efforts. Of the choices they offered, none really struck me as especially suitable for Consumer Reports, as while I did not doubt their intentions, I did doubt their ability to make a difference (some issues are just too big).
On the other hand, focusing on cell phones and good user interface design might be just exactly the right-sized problem for these folks to tackle. Guidance in choosing easy-to-use cell phones will surely help out a lot of consumers, and the number of consumers involved is enough to make manufacturers pay attention. I can hope :).