One of the beauties about practicing ANYTHING, is that over time you get good at it, and if you get good enough, that function moves from the part of your brain that does active, conscious processing, to that part where it is easily handled by one's subconsciousness.
My wife thinks I maintain a "high orange" level of SA. To me, it's a mild yellow. No great efforts on my part are required to process the stimuli I am receiving to make assessments as to my security health, I don't feel constantly wired, hopped up or paranoid (just don't ask my wife!
), and I no longer get fatigued by having to constantly filter what/who is going on around me.
Yes, my levels of awareness/alertness are tailored by my own risk assessment. Am I in the car at night on Interstate 95, 2am in the morning with windows up, very few other cars out? (I am still looking for DUI drivers!)
Am I at home in the basement, all doors locked, monitor for my security cameras right in front of me?
Or am I at the mall with my family 2 minutes after that high school let out, and those brawling prone wanna be gangster 11th and 12th graders are all over?
I hope I answered your question.