You can't think about presence, and the mind can't understand it. Understanding presence is being present.
The Truth is far more all-encompassing than the mind could ever comprehend. No thought can encapsulate the Truth. At best, it can point to it. For example, it can say: "All things are intrinsically one (The Pearl of Great Price)." That is a pointer, not an explanation. Understanding these words means feeling deep within you the truth to which they point.
A built-in reminder is the simple understanding that whenever any kind of unhappiness arises, you know you've lost the now. That's a built-in alarm clock. The moment you realize you've lost the now, come back to the now.
