@chengnay Thank you so much for the reply. I have tested it in Teleport Scene of VIU example in Unity 2019.2.
However, trackers' button can only be detected when there's no controllers connected.
Once with controllers connected, the trackers either take over the role as controller or would not be able to be fire button press (trigger, menu, etc via pogo)---at least the button press couldn't be detected in VIU.
Did I miss anything for setup?