Available just on some beta versions, WhatsApp has finally introduced two factor authentication, a feature which was long due now. If you are running WhatsApp beta 2.16.341 or above, you can enable the two step verification for added security. 
To enable, head over to Settings > Account > Two-step verification and tap on ‘Enable’ after which you will be asked to enter a 6 digit pass code which will be asked each time you try to register WhatsApp with your number. Entering the pass-code will lead to the window asking your email for recovering your pass code. Post that, a window displaying ‘Two-step verification is enables’ will appear after which you will get an option to either disable it, change pass code, change email address.
This two-step verification will now prevent anyone logging into your WhatsApp account even if they have access to your phone number. Every time one registers WhatsApp, he/she would be asked to enter the six-digit pass code associated with that number.
Another addition which should have been there long back was the ability to play audio messages in the background. Playing audio messages on WhatsApp required us to stay on that particular chat window up till now but thankfully now we can scroll through other chat windows or even switch apps while listening to the audio messages. Audio messages on WhatsApp don’t only mean voice messages but also audio files sent via WhatsApp. Earlier, in order to listen to it in the background on had to play it via music player.
Note, as mentioned before, these features are only available for WhatsApp beta users. In order to be one, go to this link and enter your email address. Soon you will get an update via PlayStore.