Rain or Shine? Smartphone Batteries Can Tell

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The same temperature sensors built into smartphone batteries that prevent them from overheating can be tapped to reveal accurate weather data better than stationary weather trackers. A team of smartphone app developers is now planning to crowd source that information for real-time temperature readings in major cities.

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James Robinson is the cofounder and CTO of OpenSignal, an app development group based in London. Currently the OpenSignal app for iPhones and Android devices is a crowd-sourced effort to build a comprehensive database of cell phone towers, cell phone signal strength readings, and Wi-Fi access points worldwide. OpenSignal strips out identification information from most of its 700,000 active users before uploading the signal data to their servers.

Recently Robinson wondered if smartphones running on 4G networks ran hotter than those running on older networks, according to the American Geophysical Union. Since the batteries contain sensors to prevent overheating, they can reveal temperature data for the phone. That curiosity led him and his fellow app developers to look at London weather data. They discovered there was indeed a correlation between smartphone temperatures and air temperatures in major cities.

“It was amazing how easily the correlation sort of popped out,” Robinson told the American Geophysical Union. “We didn’t do any handpicking of data — it sort of just emerged.”

Robinson collaborated with weather and computer science experts to develop a way to systematically calculate outdoor temperatures from the typically hotter battery temperatures. While fluctuations do occur, with enough phone data you can get a far more accurate weather picture. Robinson and the researchers recently published their findings in the journal Geophysical Research Letters (abstract).

While there are all kinds of weather monitoring sites in major cities now, they tend to be stationary and provide a single point of reference. Adding data directly from millions of smartphone owners could transform weather prediction.

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Currently the OpenSignal group has an OpenWeather app that collects weather data from users’ smartphones. The next challenge will be to fine-tune all that weather data so it’s accessible and accurate enough for forecasters and researchers. When the weather takes a turn for the worst, every extra second to get to safety can make a difference for whole regions. Smartphones indeed.

Photo: Smartphone app developers are working on a way to use the batteries’ built-in temperature sensors as a way to effectively crowd-source weather data. Credit: American Geophysical Union.