https://techcrunch.com/2019/11/20/apples-iphone-11-pro-battery-case-sports-a-new-camera-button/

Apple just released the iPhone 11 Pro’s battery case and it comes with surprise: a button for the camera. This is a minor, but welcomed addition to an otherwise standard battery case.

The button is clever. It’s located on the bottom half of the case is not a soft button that presses something on the phone. This button is exclusive to this case and when pressed, launches the iPhone’s Camera app even if the iPhone is locked. A quick press takes a photo and a longer press takes a QuickTake video.