Double Press the Power Button of Your Android Device to Start the Camera.
Your phone is probably the simplest camera you can get your hands on. To cut your camera startup time by precious seconds, double-press the power button on your device.
Most Android phones have a way to quickly launch your phone, such as the Moto X shake gesture or a shortcut on the lock screen. However, as far as Android Marshmallow is concerned, all Android phones can start the camera with a double press of the power button (unless the manufacturer has removed this feature for some reason). This is one of the quickest ways to launch the camera app, no matter what you’re doing with your phone right now. You can check the How-To Geek post below for other Android shortcuts you might not be using.
Best Android Shortcuts You Probably Don’t Use | How-To Geek