Even with end-to-end encryption on board, WhatsApp can do little to stop people from reading your messages should they manage to get into your phone. According to a report by Android Authority, a future update to the app will permit users to enter a six-digit passcode should they wish to shore up local defense against intrusion.
Apparently spotted within a WhatsApp translation program, strings include references such as 'Enter the current six-digit passcode', 'Passcodes don’t match. Try again', and 'Enter a recovery
Of course, just because the feature is being tested, this doesn't necessarily mean that it will roll out soon, if at all. But with Facebook / WhatsApp clearly ramping up efforts to make these services as watertight as possible, it's difficult to see why it would be held back.