Apple released iOS 9 less than one week ago and the update includes a new feature called Facedown Detection.
When you put your iPhone facedown, the device will no longer light up the display when you receive a notification, which in turn helps to improve your device’s battery life. In order to do this, Apple makes use of a wide variety of sensors located in the iPhone, including the ambient light sensor and proximity sensors. This allows the feature to work on all surfaces, including glass.
The Facedown Detection feature is only available on the iPhone 5s, iPhone 6, iPhone 6 Plus, iPhone 6s, and iPhone 6s Plus. If you have an iPhone 5, iPhone 5c, or iPhone 4s, the feature will not work. This is probably due to the lack of sensor support. Even though every iPhone ever released has an ambient light sensor and proximity sensor, the sensors used on the older models were probably not as capable.
It is also possible that Apple is using the motion coprocessor in order to detect if the device is facedown. This would be a possible explanation for the feature not existing on the iPhone 5 and 5c, in addition to the iPad and iPod Touch. It appears that the feature can be disabled by disabling fitness tracking, which would confirm that Apple is using the motion coprocessor to detect the orientation of the device.
It is important to note that you can’t directly disable this feature from the Settings app. Although, it is unclear as to why anyone would want to disable it, since it helps increase the life of your battery on a single charge.
[via iPhone Hacks]