This post will show you how to secure your WhatsApp by setting a fingerprint or face lock for your WhatsApp even when your phone is open. Your WhatsApp privacy and confidential chats are not secure if your phone is unlocked to another person. For instance you can give your phone to another person to watch a video unknowingly to you that the person has switched to WhatsApp to read your private chats, to protect your chats you need to setup fingerprint or face lock on your WhatsApp.
Open WhatsApp settings, go to ‘Privacy’ and select ‘App lock’

Toggle on ‘Unlock with biometric’ you’ll be prompted to unlock WhatsApp using your current bio-metric unlock pattern (mostly either fingerprint or face), unlock with the type you are currently using.

Set the automatic lock during to either immediately, after 1 minute or after 30 minutes. You can also choose to show chat content in notification while WhatsApp is locked.