the sound of the slide racking on a shotgun speaks a universal language, whether it is a .410, 20 ga. 12 ga, or boss hog 3 1/2 inch magdumb 10 guage. It tells people the reason the door was locked for the intruder's safety, not yours.
Im of a different opinion on this.I dont want an intruder knowing my location,until im ready to fire.If i choose,i can scare them with my voice,right before i fire or to tell them its time to give it up and go prone.If they know my location before i have the upper hand,then they know where to start firing and could get a lucky shot.Tweakers are known to just start firing at any sound.