Screen Off and Lock
Some apps don’t exactly scream out “rocket science,” and Screen Off and Lock would fit into that category. But it’s a neat, simple way to shut a device down quickly, and lock it, when you’re in a pinch.
(It also has a neat feature that allows you to make the screen turn to static as it’s shutting off, just like an “old time TV.”) The icon can also be dragged and dropped into the bottom navigation bar on some Android devices. It’s a free app that accepts donations via PayPal.