Touching display

If you have no human touch interface such as buttons on screen (just a dumb display showing graphics) then you can make a transparent png image at the resolution to cover the whole screen. This can then trigger an IDC which you can log, for example. 

Multiple transparent png images could be tailored to fit around given sections of a display if you do have on screen buttons, but it gets a little bit messy with triggering an IDC, but is possible.

I don't think there is an internal system information trigger that gives you the ability to sense a touch anywhere on screen unless its a dedicated button, someone else may be able to confirm. This would be a useful feature to add though...we have needed it in the past for a screensaver function we designed that has more sophistication than the built in one. We got around it with transparent png panels as above.