The left hand side of each row in the control system list contains a coloured bar that indicates the control system connection status. A green bar indicates that it is connected, a grey bar indicates that it is disconnected. Swiping down on this list will refresh the details, as well as the connection status.
The control device page also displays a 'connected' or 'disconnected' status underneath the image. This is useful in determining if lighting commands can successfully be sent to the device. The connection status automatically updates in the background while on this page.