WhatsApp has a privacy feature called Chat Lock. It basically locks specific chats and hides notifications from those chats and can only be unlocked using the same passcode as your phone, or using biometrics like fingerprint or facial recognition.
While that’s fine, the problem is if someone knew your phone’s passcode, they could open those chats. This is why WhatsApp has introduced a new layer of security called Secret Code. This will allow users to lock chats using a code that is separate to their phone’s passcode.
This means that in the event someone knows your phone’s passcode, the chats locked with Secret Code still cannot be opened, unless for whatever reason you choose to use the same code as your phone, in which case it’s kind of pointless. These chats will also be hidden and users can search for their hidden chats by searching “Secret Code” in the search bar.
This feature was discovered in a beta version of WhatsApp not too long ago, but it looks like it’s now ready for prime time. At the moment, the feature is in the process of being rolled out to users as we speak. This means that if you don’t see the feature available to you yet, don’t worry as it should eventually reach you in the coming months.
Source: Android Authority