WHEN an earthquake of magnitude 6.0 struck Northern California on August 24th at 3.20am, it not only shook the ground—it also shook people awake. Strikingly, it is possible to identify the tremblor’s epicentre by measuring the disrupted sleep suffered by thousands of people in the area who use a bracelet pedometer and sleep-tracking device made by Jawbone (see chart below). The company spotted trends in how long it took people to return to their slumber, and noted that 45% of people within 15 miles of the epicentre were unable to go back to sleep at all.
The fitness-tracking devices—often called “wearables” or “wearable computing”—emerged on the tech scene a few years ago. They promised to transform the burgeoning field of personal electronics: calculating the number of steps walked, calories burned or hours slept. After all, as computers get smaller and closer to people’s bodies, gadgets for self-tracking seemed the next logical step beyond the smartphone. By 2013 they were a $238m market around the world, with products by Fitbit, Nike and Jawbone accounting for 97% of all smartphone-enabled tracker sales. Yet despite the fascinating data that can be collected from them, like patterns of behaviour during an earthquake, the devices still have a long way to go to match the early optimism that surrounds them.