WhatsApp's newest feature: read notification

WhatsApp is already starting to enact features similar to Facebook.

Now, the messaging app acquired by Facebook has checkmarks to show that a message has been read. It also shows when a message has been delivered.

WhatsApp wrote about this in the Q&A section:

In a group chat, the second check marks will appear when all participants in the group have received your message. The two blue check marks will appear when all participants in the group have read your message.

If you only see a single check mark next to your message, there is likely nothing wrong with WhatsApp or your phone.