Pop Locker replaces your phone's standard lock screen with something with a different aesthetic. It's customizable and secure, on par with or better than the default lock screen (particularly for older operating system versions). Mostly notably, though, it extends its privacy features to other apps and to the rest of your phone.
Pop in, pop out
Here's the basics of Pop Locker: you can set a password or pattern lock for your lock screen, customize it, and even have its background change throughout the day. Aesthetically, it's pretty standard (though the default is notably good-looking enough it might be worth using). What it really does, though, is let you hide apps from prying eyes with their own passwords. By default, this locks many different apps, including your phone functionality, behind a password lock. Via the app's settings, you can improve this security further or dial it back for your comfort. It even has live themes!
Keeping security in mind
If your goal is just to hide the existence of a certain app on your phone from prying eyes, you may want something simpler. But if you want a good-looking lock screen and a great overall privacy improvement, Pop Locker will work great. Just be ready to learn how to use the app, and configure it a bit!