Just to confirm, by "pen laser" do you mean the zSpace's stylus? Assuming that is what you're talking about, my next question would have to be "what button?" Again, I'll make an additional assumption that you're developing within Unity, using the zCore plugin. We don't currently have a publicly available system to enable stylus interaction with UI elements. You'll have to develop your own way of firing UI events based off of the stylus ray relative to your UI elements. We'd recommend doing a mix of deriving a new input module off of Unity's StandardInputModule and encasing the UI elements in colliders that the stylus ray can cast against. If you just need something quick and dirty, I'd recommend just enabling mouse emulation on the zCore prefab until you can fashion a UI interaction system that suits your needs.