so I haven't seen anyone talk about this but I just went through an iOS 9 training for where I work and one of the features listed for the new battery enhancements in iOS 9 is when the phone is face down, it will not light up the screen even when a notification arrives. The phone uses the ambient light sensor for this. I thought it was kinda cool, definitely not ground breaking or new to the industry, but I've not seen that as a talked about feature online either.