A free program for Android, by SAS LABS.

Smart App Locker is an easy-to-use, fast, and free utility that can lock any application on your device with a simple password. The tool offers a variety of locking options, which include the ability to restrict access to the application for a certain period of time. You can choose to allow or deny an application to be locked.

The application supports a wide variety of operating systems, and can be used on both mobile and tablet devices. The tool is compatible with Android versions .4 and higher.

Smart App Locker is a free utility, and you will not need to pay a penny to use it. The tool is extremely easy to use, and you will not need to install any other applications to utilize it.