IME, a good alarm system works as not only a deterrent but also a preventative. I've responded to many "Alarm calls" to find the front or back door kicked in and the alarm going off. The Sound of the alarm definitely stopped the burglar before making entry.
For my personal home security, I have motion detector flood lights around my house, evil likes the darkness. I have a good alarm system with every door and window contacted, in addition I have interior motion sensors. Another thing we do is actually turn the alarm on and use it.
I live in a very nice development and their are few burglaries or break ins, but it does happen occasionally. The biggest thing I see are vehicle larcenies and that happens everywhere. I do not leave my cars unlocked in the driveway.
I also have three dogs, two will absolutely engage and fight a person. They have a whole bunch of real bites between them. My third dog, a female GSD from super working lines would not bite a person for real. I am very objective when it comes to evaluating dogs, especially my own. I understand their strengths and weaknesses. I train my two male dogs regularly to engage a person and fight with serious intensity. With that said, most dogs will not engage a person for real. It has been bred out of our dogs for thousands of years. I understand that we, as dog owners all love our dogs and think we have the greatest, toughest and bravest dogs in the world. The reality is that a kong and pocket knife will take care of 95% of the dogs out there. People need to be realistic and honestly evaluate their dogs, and realize the strengths and more importantly the weaknesses in each dog, they all have some.
Having been on the street and having met some unsavory characters that have been willing to fight and challenge my dog and myself. I know that the vast majority of dogs, GSDs included would not rise to the occasion and actually fight and win. If you have never seen your dog react to being punched and kicked in a real fight, well you just don't know how the dog will act. Barking at a person is a great thing and many folks think they have a man stopper because he scared a "bad guy" away by barking. That is not always the case.
I firmly believe that a dog that barks is a integral part to a home security plan, but it is only one part. The alarm, the lighting and the dog are all needed. Then a plan to call the police, a secure place to go is also needed and perhaps a means to defend yourself if all else fails. Please do not rely on an untrained dog that barks to defend you, you may wind up being very disappointed.