Avast is one of the top mobile protection and antivirus app. Most of the antivirus features which this app attain are free, but the premium version (costs $14.99 per year) allows you to access the extra features such as app locking and advanced theft detection technology.
Avast scanning process searches for the other installed apps you have on your system by default, other than the system settings and each and every file saved even those which are stored on your SD card.
Along with this, any of the apps you install on your system will automatically get scanned for any virus during its installation.
Avast’s anti-theft features are free, but they need the installation of an additional app to work properly.