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 Early warning systems can be the difference between life and death in earthquake-prone regions. But they are expensive. The US, Mexico and Japan have such systems. That leaves large swats of central and South America, Asia and the Caribbean unprotected. Now scientists think one solution could be hiding in our pockets, our cell phones. Smart phones employ the latest GPS technology. So scientists tested arrays of smart phones to determine if they could measure the displacement¹ caused by the earth shaking and signal the subtle beginnings of an earthquake. For the experiment, the researchers used a hypothetical Magnitude 7 earthquake in California and data from the real Magnitude 9 earthquake off the coast of Japan in 2011 that led to the tsunami² that caused the nuclear accident at Fukushima. They found that as few as 500 cell phones in California could alert the public 5 seconds before an event, enough time to at least move to a less vulnerable part of a room or dive under a desk. For the Japanese earthquake, early warning would not have helped in the region closest to the epicenter, but such an alert could have helped cut damage in downtown Tokyo, and the information would have reached the coastline life-saving minutes before the resulting tsunami waves did. The researchers in the Journal Science advance this. The scientists say various technological³ details need to be worked out, such as how companies would allow smart phones to access and share the raw data. They point out that instead of waiting to buy expensive top-grade scientific equipment, governments could consider creating interim⁴ early detection systems based on arrays of sensitive smart phones.