Instagram and Messenger could soon follow WhatsApp in introducing encrypted messaging as part of Facebook's plan to unify its app empire. In the meantime, WhatsApp is adding an extra layer of privacy on iOS with support for Touch ID and Face ID. The update (version 2.19.20) allows users to lock their messages behind their iPhone's biometric authentication features. You can switch it on by heading in to settings, selecting Account, Privacy and "enable Lock Screen." You'll then be able to set a time limit immediately, after a minute, 15 minutes or 1 hour.
It's important to note that the new feature doesn't work on a per-chat basis and instead locks up the entire app. Notifications will still appear on the screen if you have them turned on, allowing you to quick-reply to messages. You'll also still be able to answer calls. Touch ID is available on the iPhone 5S and beyond, while Face ID is available on the iPhone X and later.