I hear that guineas sound a pretty good alarm, too, but I'm not sure about nighttime. Some birds are nightblind. But they are noisy without strangers around, so I wonder how you would tell the difference?
A "Beware of Dog" sign when you have a dog is an invitation to a lawsuit. It is advertising (rightly or wrongly) that you know you have a vicious dog. Better is a "No Tresspassing" sign, legally.
Don't leave your door unlocked. Just because you trust your neighbors doesn't mean you can trust any bunch of joyriding teenagers or meth heads looking to score something they can sell.
Sue