The door question asks whether you are here. These three questions go further. They divide your attention three ways, so that less is left over for sleep.
The first is about you. Who is here? What am I doing, and why? What am I thinking and feeling right now? This is watching yourself, gathered into a single moment.
The second is about what you are looking at. Whatever is in front of you, a cup, a face, a tree, see it as if for the first time. Not the label in your head, but the thing itself.
The third is about where you are. This room, this street, this hour. Look around and ask honestly where you are. Sometimes the place suddenly looks strange, as if you had just arrived. That strangeness is a good sign. It means you are seeing it.
The tradition calls this the key of SOL: subject, object, location. When attention rests on all three at once, the energy that usually leaks into daydreams is kept. The books say that kept energy is what wakes us.
Try it for a few seconds at first, then for a minute. You will forget, and then remember. Each remembering counts.