To be properly engaged you must achieve a state of active seeing and active listening. In addition you other senses must be engaged as a supplement to the two main senses of sight and hearing. If you are engaged this way you chances of survival in a violent encounter increases exponentially. It goes from bad to good real fast.
Most of today's population walk through life distracted by inner thoughts and concerns. In addition there is a growing tendency to disengage from every day life using electronic devices most often connected to ear jacks shoved into the ear closing of most external environmental sounds. It tends to place folks into a disengaged victim status that can be exploited by others let alone allow for accidents and injuries.
Martial artists and others who gear training toward a defensive posture must also learn how to fully engage themselves so they can take appropriate actions to remain protected. This is even of greater importance if a person decides to work as a professional, i.e. police, military, emergency, etc.
Active engagement is not just a sensory model and it entails things like force, legal and psychological matters to name just three of many. Avoidance, deescalation, etc. all fall under this active engagement model if it is to be used fully and completely.
Add in things like awareness, diligence and listening to your instincts you can achieve various levels of engagement that can provide enough advanced warning to allow escalation of the active engagement levels to work out strategies and tactics that will avoid, deescalate and apply physical actions that remain within the legal standards set by society.