A constant high pitched "eeeeeeeeeeeeeeeeee" like a beep with no beginning or end. Mine is loud today...perhaps because of the party I had last night. As folks entered the man basement/pool room/bar area all handguns and car keys were locked in the safe until folks left with a safe ride home. I've been to too many parties where alcohol/judgment/tempers get skewwed. All my buddies carry and they are cool, but stuff happens. I may get flamed about locking up their guns, but my house = my rules. If folks don't like it, they can go home. Guns and alcohol don't mix.