The information regarding the next-generation iPhone likely including this sensor comes via Xcode 6 and iOS 8, the latest iPhone software development kit and operating system. The software includes updated CoreMotion APIs that clearly reference the new altitude measuring capabilities.
A new framework dedicated to altitude tracking has been discovered and it requires dedicated hardware, according to developers. As you can see in the screenshot below, the framework checks if the iOS devices supports reporting relative altitude changes.
FutureTap developer Ortwin Gentz says he tested the framework on an iPhone 5s. It returned 'No', indicating that the iPhone 5s does not support reporting relative altitude changes.
In addition to this framework, Hamza Sood was able to located references to ambient pressure tracking in iOS 8. This could be used to help forecast weather information.
These findings corroborate a report from a chief analyst at ESM-China who predicted that the iPhone 6 could come with built-in temperature, pressure, and humidity sensors.
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