How phone batteries measure the weather

As with many data analysis posts: Give me more information about the data. In this case it could be particularly interesting. You have correlation and you estimate the temperature through indirect measurements. The important word here: <i>estimate</i><p>As with all estimates I care about the error and not much else. The only error measure provided is <i>mean absolute error</i> which I find a little bit unsatisfying. It gives only very little information about the behavior of the error.<p>The easiest is to compute the error for every sample and then show a histogram of it.<p>Why you might wonder? In this case we deal with varying -though often over time stabalizing- data. This means that sometimes the error is actually greater and then very little. If you take the absoluate value of it and take the average (MAE), you <i>might</i> underestimate (resp overestimate) the error at times. In this case I might expect a tri-modal error distribution if we consider positive &amp; negative errors.<p>A histogram is much more expressive (and oh so simple to generate) than a simple MEAN, STD DEV, MAE or MSE.

TL;DR: &quot;If it’s cold outside, chances are temperature sensors sometimes outside are colder than usual.&quot;<p>By itself, I have to admit I don’t find this particularly surprising, especially since they both averaged over space (whole cities) as well over time: There is no data presented on how well the correlation between battery temperature and outside temperature works out within a single 24-hours-period – given that most people are asleep at 2am, this would be another factor all&#x2F;most batteries have in common apart from the outside temperature.

I don&#x27;t think this really means anything. If you track the indoor temperature and outdoor temperature at my apartment, they correlate. But it&#x27;s because I come home as it&#x27;s getting cool and turn on the AC, and I leave for work before it gets too hot out. So the shape of the graph looks the same, but the relationship is that I come home from work at the same time of day when the sun sets, not that the outdoor temperature affects the indoor temperature. (Weekends are proof, it&#x27;s cold all day indoors then :)

Do you think it possible to make smartphones into body temperature thermometers?<p>I currently have an iOS app that measures heart rate with the light&#x2F;flash while you put your finger over the camera. The camera measures your pulse by reading the difference in &quot;color&quot; or &quot;density&quot; of your blood reflecting into the camera as your Harry beats.<p>It&#x27;s not medical grade in accuracy but holds up well in comparison with the heart rate testers at the local grocery store or manual pulse counting.<p>My rough estimate is this method is accurate to a few percentage points of a real medical device.<p>For those iOS and Android developers — would it be possible to detect body temperature to accuracy levels of that of a thermometer ( +&#x2F;- 0.1 degrees ) using this battery method they are using for the weather?<p>It would be nice to check your temperature without the need for external hardware. Though even external hardware could be a great device, checking pulse, pressure, temp, and storing all data for historical analytics. Add in that you could compare that data worldwide and flu estimations may become possible. At least outbreak areas should be able to be narrowed somewhat. There&#x27;s a ton of other data that could be gathered too. Just mapping outbreaks would be interesting to see how seasonal ailments migrate. Even allergies could be mapped.<p>Thoughts?

This is cool. Possible use cases for those who are not grasping it: * Under developed countries who do not have a national weather service begin to start tracking historical temperatures.<p>* People at risk of heat stroke could have an app on there phones that alert them when the temperature is too high. (Most phones do not have a thermometer, and the temperature reading of a room with no A&#x2F;C is different than the outside temperature)

Interesting, but the temperature reading is unusably inaccurate from my location. 3 degrees C can matter a lot when it&#x27;s around the 20 C mark.<p>Cool graphs though.

Possible to track average change in battery life from temperature difference? That&#x27;ll interest me more.

1) there is so much room for error that it makes improving it not worth it 2) there are already many other devices with better readings and already in place<p>I guess I&#x27;m missing something? ...or is it just a proof of concept (when it&#x27;s cold things get cold)?

TL;DR: a phone&#x27;s ambient temperature and a phone&#x27;s temperature correlate.

It is surprising that a temperature sensor is reading the temperature?

Battery temperature rises with bad roms and excessive gaming and apps , did you consider all these conditions. It&#x27;s really complicated.

All of the readings are skewed by air conditioned buildings.

I started to lose respect for people commenting on this board...I don&#x27;t see what is the big deal with this, and why would you even publish a paper on it.<p>Here is the thing: Temperature reading of battery may not even be the actual temperature value of the battery. Even the circuits itself that read temperature is sensitive to temperature (they have the same correlation with temp. as battery..Higher the temp. is, higher the leakage current, and hotter your device will be). So temperature reading itself will be combination of things, most of which have similar correlation against temperature of the environment. This is a well-known fact to all people working in semiconductor industry and we simulate things against temp. all the time.<p>And when you average out thousands of reading from different cell-phones, you will get rid of all those noise coming from phone-usage, whether person holds the phone or keep in in his pocket ..etc.<p>As a side node, if the batteries in each cell-phone made by different manufacturers, their temp. reading will also be different and will add a noise as well.<p>You built an app to read temp., OK fine. But, it just annoys me the fact that they talk about it as if this was a new discovery, and publish a scientific paper about it :)