How to access the hidden pressure sensor built into your iPhone

Since the release of the iPhone 6 and 6 Plus in 2014, most Apple smartphones have included a built-in barometer. This hardware measures barometric pressure to help determine relative elevation changes and assists features in the Health app, such as step counting and stair climbing. Apple does not include a standalone application to view these measurements directly, and its native Weather app relies on external data sources instead. However, developers can access altitude and pressure information through Core Motion. Users who want to view direct readings from the internal sensor can download third-party software from the App Store. Applications such as Barometer & Altimeter & Thermo and My Altitude explicitly utilize the on-device pressure sensor alongside GPS and weather station data.