This application requires you to set up a password the first time. On providing the READ_CONTACTS permission, it will detect the WhatsApp contacts and list them. You can then lock any one of them by clicking the lock icon next to a contact. To lock groups, you have to use the Plus Icon in the bottom left corner. This app does not have the Internet Permission. So be rest assured, no data is transferred over Internet.
This application enables users to lock their selected WhatsApp conversations with a password without locking the entire application. Fingerprint authentication is also supported for devices with fingerprint sensor.
For phones having Android other than the stock versions( Redmi, Honor, Oppo) you need to lock the app in memory such that the background service is not killed by android.