In the early morning hours of February 2025, cell phones in S\u00e3o Paulo, Rio de Janeiro, and Minas Gerais rang simultaneously, announcing an earthquake of up to 5.5 magnitude. Many people woke up in panic. The earthquake did not happen.<\/b> \u2014 no seismological institute recorded anything.<\/p>\n
The episode explains better than any manual what this alert is and what it isn't. It's real, it's free, it comes pre-installed on your phone, and it can save you precious seconds. And it's wrong sometimes, because the price of warning you in seconds is giving up certainty.<\/p>\n
The earthquake sends a weak wave ahead and a destructive one behind. Because the internet signal travels faster than the wave, it's possible to warn those who haven't yet been affected.<\/p><\/div><\/div>
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The accelerometer that rotates the screen also senses vibration. When thousands of devices vibrate together, the pattern ceases to be noise and becomes detection.<\/p><\/div><\/div>
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The window of opportunity is short and shrinks as you get closer to the epicenter. It's for getting away from what's falling, not for evacuating the building.<\/p><\/div><\/div>
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No technology in the world can predict tomorrow's earthquake. Every app that promises to predict earthquakes is lying, without exception.<\/p><\/div><\/div> A system that needs to make decisions in seconds, based on common cell phone sensors, is bound to make mistakes from time to time. The alternative would be to wait for confirmation from a seismological institute, and then the warning would arrive after the tremor, which is useless.<\/p>\n After the Brazilian incident, the system was deactivated in the country, reviewed, and reactivated with stricter criteria. That's how these things mature\u2014and that's why knowing how to interpret the alert is just as important as receiving it.<\/p>\n
\n<\/div>\n<\/i><\/span>Understanding how the alert works<\/span><\/a>\nWhy it's wrong \u2014 and why it's still valid.<\/h2>\n