How Android phones became an earthquake warning system

If you're the owner of an Android phone and live in a seismically active region, there's a chance your phone has popped up an unusual warning. Not one that asks for permission to share personal information, or potential malware, but something far more serious: There's an earthquake nearby, and you have up to a minute or two to get to a safer location. Starting in the US in 2020 and expanding internationally since, the system is called Android Earthquake Alert (AEA), and it's on by default in most Android phones. And today, Google has a paper in Science that describes how the system works, how the company has improved it, and what it has seen during the first few years of operation, including what caused a handful of false alarms. Shaking things up Smartphones come with accelerometers, small devices that enable them to sense changes in motion. This is how they manage to do tricks like figuring out how many steps you're walking. If your phone is sitting quietly on a table, however, the accelerometer shouldn't be registering much significant motion. But anything from you walking across the room to a truck going by outside can cause vibrations that your phone's accelerometer can pick up. As can the often less subtle vibrations of earthquakes. Part of the system Google has devised is a method of telling the two apart. And part of it is using that determination to alert people with enough time to do something about the impending arrival of potentially destructive seismic waves. If you happen to be right near the epicenter, your phone will be among the first to pick up the shaking of the earthquake, and there's no way for an alert to do you much good. However, your phone could potentially help others, as the vibrations that it senses move through the Earth's crust at speeds that are relatively slow compared to the sorts of low-latency signals that convey information on the Internet, some of which operate at the speed of light. That means the phones that are initially shaken can be used to trigger a system that will get off a warning that can potentially reach other phones seconds or even minutes ahead of destructive seismic waves.