WhatsApp aims to increase the privacy of its users and, for this reason, the iOS version of the application is currently experiencing a test phase to unlock the application using footprint digital or by using Face ID (face recognition).
This feature allows you to “lock” the application until the owner of the phone is identified by either means. Once done, you can set the interval at which the login will remain valid, before a new block.
Furthermore, when the application is blocked, it is not even possible to peek at the contents messages from the multitasking page, where the preview of WhatsApp is replaced by an entirely white page.
Once the tests are finished, this function should become effective with the next update.
Source: iSpace
