What is the best app for Android devices? Why?
You'd better use a security app to protect your android devices, i'm using AppLock. Maybe you can give it a try.
The app itself is a simple, but powerful app that allows you to lock your apps with number password/pattern password/fingerprint, so that snooping eyes can't see them. This is great if you have nosy roommates, kids, or if you just want some piece of mind.