WhatsApp is probably working on two-factor authentication. The function works with a six-digit code that must be invented and remembered by the users themselves. How this new WhatsApp authentication will work is still unknown.
The Twitter account WABetaInfo found the hidden function in the latest beta version of WhatsApp for Android, 2.16.183. The function works with a code created, modified and deleted by users. If a user forgets a code, he can access his account through a predefined email address.
WhatsApp will add the two factor authentication feature! (HIDDEN FEATURE OF ANDROID 2.16.183 BETA) pic.twitter.com/gucgjfjOwz
— WABetaInfo (@WABetaInfo) July 19, 2016
It is not yet known how and when WhatsApp will use the feature. Standard WhatsApp sends a generated code via SMS for authentication. After that, WhatsApp calls on the same phone for once which is not for authentication. It could be that the function is used to restore from backup when logging on to a new phone. To use WhatsApp Web or desktop is done via a QR code to scan users in the app.
It happens often that WhatsApp tests features in beta version and those appear in the real version much later. The existence of many new features coming for the first time to the outside through the betas.