Colonel Jeff Cooper's color code, developed for combat marksmanship and now standard in civilian, law enforcement, and military threat-awareness training.
Stay in a state of relaxed alertness so the first sign of trouble is not a surprise.
Condition White is oblivious - headphones in, eyes down, mind elsewhere. It is a fine state at home behind a locked door and a dangerous state anywhere else.
Condition Yellow is relaxed alertness: you notice who enters the room, where the exits are, whose hands you can see. It is not paranoia. It is respect for the environment God placed you in.
Orange escalates to a specific concern - that person, that vehicle, that behavior. Red is the decision to act. Trained warriors live in Yellow, move to Orange without hesitation, and only ever visit Red when they must.