How Does He Know?

How does he know?  How does Rowdy sense when I am about to do something and he jumps up to follow me?  What nuance do I have?  What body language do I present?  What is it that he tunes in on?

There are certain repeat behaviors that I do, when I am about to go do something.  When I go to bed and turn off the computer, there is a Microsoft sounds ding at shut down that when it goes off, he jumps up to follow me to his bed, which is his dog crate close to my bed.  He knows that when he hears the ding, I am going to get up out of my chair.  But lately, if he is alert, he will jump up when I am only clicking on the shut down icons before the ding.  How did he know I was clicking to shut down?  I could have been clicking on anything like a Youtube video, or an item on eBay or Craigslist.  What did he sense to know that I was shutting down and going to bed?  Where he lays, the computer monitor is out of his direct sight, but he has proven to be blind to what is on the screen, so he can't see the change on the screen when I log off the internet to shut down, so how did he know?

Another scenario; When I am out working in my workshop and I am going back to the house, before I am ready to walk out the door, he jumps up off his pillow to follow me.  This was when I first noticed it and have been monitoring my behavior, to try to determine what causes it.  There are two main signals that he usually tunes in on and jumps up to and those are when I take off my glasses and/or pump the bottle of hand cleaner.  But, when I don't do those things and are about to run to the house for something, he will still jump up.  What did I do that he tuned in on, to know that I was going to the house?  I'm moving around a lot and move toward the door many times in my movements, but I am not leaving the shop.  In this case I may not remove my glasses or pump the hand cleaner, but still he knew that I was going out the door this time and jumps up to follow. 

Depending on what I am doing, I may take my glasses off several times too, but he doesn't jump up till I am ready to walk out the door.  How did he know that was in my thoughts?  How did he know at that particular moment that I was heading for the house?  Did he read my mind, or was there some subtle change in my body language to signal my intent?  How does he know?