A few weeks ago, WhatsApp introduce the Read Receipt features. To make you able to use this features, all you need to do just update your WhatsApp application. But due to some feedbacks relating with the privacy of WA users, at Saturday November 15, 2014 , WhatsApp added and introduced a new feature that make you able to control whether you wanna activate “Read Receipt” feature or not.
If you disable the “Read Receipt” feature, whenever you read the messages that you’ve received, the sender of the message would receive blue double-mark in their device.
According the offical WhatsApp website, you need to download the latest version of WhatsApp to get this ‘disable feature’. As for my personal experience, the WhatsApp 2.11.444 is needed.