Is there a way of getting an event or slot called when a modifier key such as Shift, Ctrl, or Alt has been pressed regardless of what widget currently has the focus?

So the user presses the left Shift button and an event handler gets called to tell the app that the shift button has been pressed. It doesn't matter if it can't differentiate between left shift and right shift.

It is important that the widget doesn't need focus in order to get the event.