I have a sign posted so people do know that we have dogs, (in case they can't see the one in the front yard, duh) they are well mannered dogs and great with kids, (as I have smaller children myself) and a wonderful addition to our family.
My dogs have not been taught to KILL, but they have been taught to PROTECT!! And I believe that's exactly what they do, I understand if my dog were to harm someone I'm at fault, but that would only happen if the dogs felt that our family, home or themselves were in danger. And as far as that goes, if the "would be" thief was stupid enough to continue into my home, then he/she deserves to be met by the "house patrol," so to speak.
Anyway, yes we have a security system, and I believe everyone should, but the dogs are just an added measure of security, considering computers, electronics, etc are not 100% accurate.