I am looking at quite a few on line but I want the alarm to only sound at the receiver end. Plus, as I read about them I am wondering how sensitive they might be. If it is in Dad's bedroom we would like it to go off when he leaves the room and not scare him. But if it is too close to his bed will it go off when he roles over? Do they make ones that are more straight line passing through and not like an arc or a radius? I have looked on Amazon and Home Depot and now I am confused.