one can build, but is it worth it? could we really compete price wise to an asian built alarm system? personally, i don't think so, but great idea.
But to narrow things down.
perimeter sensors, autostart, mp3 (voice siren), gps are already available out there with present day alarm systems. just some of these units are mad expensive.
Camera is something we are probably just better reverse engineering and making it work with the siren output of an alarm system, but there are at this moment too many complications with such a thought as to how to get this to work.