You are always ready to engage in combat. You gain advantage on Initiative checks and Wisdom (Perception) checks that rely on hearing, as well as +5 on your passive Wisdom (Perception) (not cumulative with other similar bonuses, including ones gained from other features.). And you may add your proficiency bonus to your Initiative checks.
In addition, you can't be surprised while you are conscious and other creatures don't gain advantage on attack rolls against you as result of being unseen by you.