The end of the 'fat finger' problem? Why the back of your smartphone is about to become very useful

The underside of your phone could soon take a screenshot, lock the phone or answer a call

The smartphone is at the centre of our digital lives because of its countless interactive possibilities, but more than half of its surface is dead. Take a look at the back of one, and you are unlikely to find much beyond a logo and a camera lens. If you touch, prod or swipe it, it will do nothing. This, however, could be about to change.

After more than a decade of patents, academic papers and tentative technological explorations, the rear side of the smartphone may be about to do something useful. 

<span>The good news is that the index finger on the back is at least as efficient for pointing and swiping as the thumb on the front</span>

The hint came at Apple’s annual conference for developers, which took place last week in an online-only format. Most of the noise was about new operating systems ushering in features such as instant language translation, digital car keys and much else besides. But there was an upcoming iPhone feature that was not mentioned during the keynote, called Back Tap.

Hidden away in the accessibility settings, it will convert taps on the back of the phone into actions. You could take a screenshot, lock the phone, answer a call or even remotely control home devices. Those who have had a preview say it works through a case, too. 

This could be a game changer, not only for people who can operate their phone with only one hand, but also for anyone who prefers to do so. This method of interaction has been hampered in recent years by the ever-increasing size of smartphone screens. Posture and ergonomics experts advise against it, but sometimes we have little choice.

“One-handed use is very valuable in certain situations,” says Jacob Wobbrock, professor of human-computer interaction at the University of Washington. “We’re accustomed to using the thumb on the front of the device, but the good news is that the index finger on the back is at least as efficient for pointing and swiping as the thumb on the front.”

Researchers discovered this more than a decade ago. On the earliest touchscreens, which were small by today’s standards, touching specific points was not easy. It was known as the “fat finger” problem, where the finger obscures the thing it is meant to be clicking on.

While touchscreens meant the end of physical buttons, the irony was that on-screen buttons had to be larger than the ones they were replacing.

Studies established that “rear touch” could be the answer. Moving a finger across the back of the device, controlling an on-screen cursor, could then eliminate the problem in its entirety.

Researchers at Microsoft also noted how a touchable back panel could allow you to control some of your phone’s features without even looking at it – say, when it’s in your pocket, or bag.

In 2009, a proof-of-concept phone called the Synaptics Fuse demonstrated how this new concept of rear touch might work. “This could be how phones will look next year,” said one review. But it did not happen.

Patents were filed by Google and Apple, and rumours swirled that the iPhone 8 and Google Pixel would come complete with sensors on the rear, but they never did. Since 2010, fewer than half a dozen smartphones have ever incorporated the feature, and it has never caught on.

The reason, according to Seongkook Heo from the Computer Science Department at the University of Virginia, is simply our unwillingness to learn new ways of interacting with devices. “Many users just buy their new phone, turn it on and start using it by touching what is on the screen,” he says. “Not many people look for new features and spend time learning them.”

A number of new gestures have seen early retirement over the years for this reason, such as the iPhone’s “3D Touch” and “Air View” for the Samsung Galaxy, where a hovering finger can initiate an action.

“The best testing cannot always anticipate how end users will ultimately want to use a thing,” says Wobbrock. But technology is now developing to a point where all kinds of surfaces can be touch-enabled, and the temptation to introduce them to new phones is strong within the industry. 

Leaked images show that Huawei’s forthcoming Mate 40 Pro phone may have a circular touch-enabled area surrounding the camera lens, which could be used as a volume wheel or a camera zoom. Sentons, a US company specialising in touch technology, envisages every surface of a device becoming interactive; phones could be squeezed and imaginary side wheels could be used to scroll pages. 

For Heo, this is tremendously exciting. “If smartphones are used for more complex tasks, there will be more calls for efficient interaction techniques,” he says. “I hope Back Tap will be successful, and add more input vocabulary to our smartphones.” 

Apple is being so coy about the new feature that most people will not even notice that it exists. But for those that do, it offers an intriguing glimpse into the way our devices may function in the future. 

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