I have always made it a special point to be alert to my surroundings. We have a responsibility to ourselves and to our loved ones to be aware of danger, alert to trouble, and the like. This can be exhausting, if you don't apply your methods correctly.
To use the definitions used here I have personally primarily used a combination of two levels of awareness:
1 - Relaxed Awareness - when in places where I spend most of my time, and it's easy to be alerted to something being out of place. The office, the house, church, etc.
2 - Focused Awareness - when in places where I am not familiar, and as such things out of place are less likely to stand out to me, as 'everything' is out of place by my perspective. New settings, new city, job interviews, special social occasions, and public areas which change frequently due to layout and visitor changes such as malls, restaurants, stores, garages, and the like.
I have constantly encouraged this concept (though not worded nearly so well, or so detailed) to my loved ones.
In what level of awareness do you typically find yourself? Do you pay attention to what's going on around you? Would you be taken by surprise if someone unexpected walked in the office? Would you be unable to react if you witnessed a mugging while shopping? Would you see that box sitting somewhere that it shouldn't be?
It's very easy to be aware of what is going on around you without draining yourself. I encourage you to try!