The two ways the AI can detect the player is through sight and sound.  When the player is seen through the sight sense a variable will be set with the actors class which will allow the use of the MoveTo node which will move the AI to the selected actor. 

All sound detection comes directly from within the Animation Blueprint, for each animation I setup some notifies that will check if it's the player animations and if true will call the Report Noise Event node.

Enemy takedowns are handled through a collision in the back of each enemy. If the player is colliding with the collision and hits E the enemy will lose it's controller, ragdoll, then be destroyed after a few seconds.