I think that part of the habit with chuck keys needs to end with them in specific places after every use. Every time. It is important that we notice that we are doing something different than usual to set off the alarm bells in our head that something is wrong. I also look at the chuck key in its resting place before pushing the spindle start button. A combination of muscle memory from doing it the same way each time, along with looking at the key, which is not in the chuck, tells us that the chuck key is safe for us to continue. Random actions give random results. I prove it daily, and work on it daily...I can stretch some jobs out too. I'm so paranoid about leaving the key in the chuck, I often walk away with it in my hand to leave it sitting in random places around the shop.
I also look at the chuck key in its resting place before pushing the spindle start button
My lathe also has several chuck handles. They are all kept in the same area, behind the chuck, close to each other. All three have to be there for me to turn on the spindle.When I got my first lathe my mentor impressed on me to build a holder for the T handles in the front of the lathe and the handles only ever leave the hand into the holder. whenever it is out of the holder it is 'welded to my hand'.... never left it in the chuck in nearly 40 years.