I&#x27;m a graduate student in Environmental Fluid Dynamics and I deal with a lot of environmental sensors. The temperature sensors on phones are pretty accurate, but they&#x27;re quite sensitive to small changes. This means that nradov&#x27;s original statement is correct: Body heat and cell phone usage are absolutely going to affect the temperature sensor. For example, Sensirion makes a high quality temperature&#x2F;relative humidity sensor and they recommend the PCB have cutouts around the sensor to offer proper ventilation and minimize heat transfer from surrounding components [1]. On the iPhone 6s, the pressure&#x2F;temperature sensor is on an edge, but it&#x27;s also right next to the NAND flash chip, so I&#x27;m not quite sure what the heating effects would be.<p>I can&#x27;t answer much to your second question but I imagine it&#x27;s easier in colder environments, especially if the phone is not in a pocket. In addition, here&#x27;s a publication that claims to be able to get useful signals from noisy data, so I don&#x27;t know if I would say the measurements are useless [2].<p>[1] Fig. 10 in <a href="https:&#x2F;&#x2F;www.sensirion.com&#x2F;fileadmin&#x2F;user_upload&#x2F;customers&#x2F;sensirion&#x2F;Dokumente&#x2F;Humidity_and_Temperature_Sensors&#x2F;Sensirion_Humidity_and_Temperature_Sensors_SHT21_Datasheet_V4.pdf" rel="nofollow">https:&#x2F;&#x2F;www.sensirion.com&#x2F;fileadmin&#x2F;user_upload&#x2F;customers&#x2F;se...</a><p>[2] <a href="http:&#x2F;&#x2F;onlinelibrary.wiley.com&#x2F;doi&#x2F;10.1002&#x2F;grl.50786&#x2F;full" rel="nofollow">http:&#x2F;&#x2F;onlinelibrary.wiley.com&#x2F;doi&#x2F;10.1002&#x2F;grl.50786&#x2F;full</a>