WhatsApp launched a new security feature a few days ago that prevents others who may be able to access your device from snooping on your messages in WhatsApp .
According to Forbes magazine. The activation of the new security feature requires the installation of the latest version of the WhatsApp application (2.19.20).
After making sure of your WhatsApp version, press "Settings" then on "Account", then "Privacy". At this point you'll see "Screen Lock" and you'll have two options on the screen: Touch ID or Face ID, depending on which version of your smartphone you're using.
Once you've turned on one of the two options, you can choose when to close the app. Here you will have 4 options to close: a minute, a minute later or a 15 minute or an hour later.