We offer a companion World of Warcraft addon designed to work with the WowUp application, or any other application that would like to use it.
Currently the addon is kept in sync with the WowUp application, and will display available updates for your particular client. In order to use this addon you can search for WowUp in the Get Addons tab!
The source of this addon is freely available on GitHub.
There are several ways you can configure the WowUp addon to notify you however you like. You can modify this in the standard World of Warcraft Game Menu > Interface > Addons tab > WowUp Notifications section