If you get a lot of notifications during the day, you can actually save a bit of battery life by leaving your iPhone face down on a table or other surface.
Face-down detection is a subtle feature that Apple snuck into iOS 9 last fall to save a bit of power on modern iPhones by not lighting up the screen whenever text message notifications come in — after all, the screen is one of the biggest power consumers on the iPhone, and since you can’t see the screen anyway when the iPhone is face down, what’s the point in turning it on?
To enable the feature, simply place your iPhone face down on a table when you’re not using it — notifications will still sound or vibrate, according to your settings, but the screen will remain dark unless you pick up the iPhone within a few seconds of receiving the notification.
Since the feature uses the M7/M8/M9 motion coprocessors, you’ll need an iPhone 5s or later to take advantage of it, and you’ll need to make sure you haven’t disabled Fitness Tracking under Privacy, Motion & Fitness in the iOS Settings app.
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