WhatsApp's new Secret Code lets you add an extra layer of security for your locked chatsWhatsApp introduced Chat Lock early this year; six months later, there's an extra layer to those chats for added privacy.
Source: WhatsApp's new Secret Code lets you add an extra layer of security for your locked chats (https://www.androidcentral.com/apps-software/whatsapp-introduces-secret-code-feature-for-locked-chats)