Tom is late for his train and doesn't know the way to the station. Racing around a corner, he runs into a plaza full of tourists snapping and uploading photos to Instagram and Facebook. Which way should he go? He tells his Internet-connected contact lenses to load a map, meanwhile tapping at his smartwatch to pull up his ticket and platform information. An alarm flashes in his peripheral vision, only 15 minutes until the train departs, but the map is not loading. He looks around in dismay, frantically yelling “refresh” to his lenses against the clamour of the street. An alert scrolls across his vision: “You're feeling stressed. Take a breath. Have a hug!” But with all the tourists accessing the Internet, Tom has no hope of getting his much-needed map.

Welcome to the chaotic future of wearable electronics: devices that promise to connect real to digital lives seamlessly. These gadgets are rapidly multiplying, and within five years there could be half a billion devices strapped onto, or even embedded in, human bodies. Today, the most familiar gadgets are fitness trackers and smart watches, which monitor health and provide ready access to online services. But there are already devices that claim to do more than monitor, such as headbands that alert wearers when they become distracted or wristbands that administer electric shocks to smokers who want help quitting. Electronics companies promise to transform medicine with wearables that can treat symptoms or manage care. Devices are emerging that alert people with epilepsy to incipient seizures, help prevent anxiety attacks, and enable blind people to navigate.

But the potential of wearables crucially depends on the large amounts of data they access and generate. And that leads to two problems that researchers and technology developers are struggling to solve: finding improved ways to transmit data to and from wearables, and keeping all that information safe. With everything from toasters to cars now connecting wirelessly to the Internet, demands on a finite bandwidth are rapidly straining the system. Nearly half a billion new devices started chattering over mobile broadband last year alone, pushing mobile traffic to 25 times what it was just 5 years ago. And wearables are leading to new security concerns, from the use of highly personal data to track people's activity to maliciously attacking their online presence.

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