I just let the snick of the safety going off to terrify them :-) My 870 has one up the spout at all times.
I am not the police. If you are in my house I am not going to try to deter you, nor am I going to try to frighten you. I am going to stop you where you stand. The only warning you will have will be the light on the for end illuminating you to confirm you are a threat and a target, make to sure my background is clear, and then the snick of the safety going off. If you choose to stop immediately then I will let you. If you do not I will stop you.