Need help fixing bad alarm install

I had an alpine 8028 alarm installed at circuit city a while back.  well i realize now that it was done pretty bad and would like to fix that as well as upgrade it.  the brain is right under the dash easy to get to, so it needs to be moved, wires under the hood are easy to tell what they are, so they need to be moved. 

I also wanted to add a second siren (preferably battery backed up or a "pain generator" but how does battery backup work?), second impact sensor, and a proximity sensor.  I don't know if this can be done on my alarm or not, if not i was thinking about getting the new alpine 150 alarm. 

My question is can i add the stuff i listed above to this alarm since it only has the impact sensor input (may have 2) and a single siren out?  how can i do it? 

You can add any sesnors that you want but you just have to diode isolate each one from each other in order to reduce false alarms. The Alpine ( I think ) uses a programmed adjustment through the brain of the alarm to change the level of impact on it's sensors, but if you buy a universal sensor, just tap into one of the (-) trigger wires for the alarm and you should be fine. The battery back up you have to run a new wire from the alternator to the (+) side of the back up battery and ground at the chassis. I recommend the alternator because then the battery will charge when the alternator is running and also, it's less conspicuous than running a new wire from the battery.

cool thanks.

as for the battery backup, i wanted to get a siren that had a battery or whatever in it, so that if it was disconnected it would still go off.  can this be done or should i just hide it real good and not worry about that?  also i'd like to lock up the hood so that they can't get into it to disconnect the car battery, it seems awful hard to find many ways to do this which is kind of surprising i would think this would be more common than it is.  do you think the alarm i have is fine or do i need a new one?  if i keep this one, where could i get the sensor addons i'd need, and does it matter what brand?

i'm thinking it'd almost be better to just get the new alpine alarm off ebay for 150. then i'd have two sirens (no battery backup though), and two impact sensors and the motion sensor.  it should plug right in i'd think and this way the motion sensor will work with the brain like its supposed to as i don't see how it would work very good if connected to a brain that doesn't really support it. 

It's up to you if you wish to get a backup siren. They are universal application devices so they will work on the Alpine alarm. The 8028 is a decent alarm system, but if you want more options with better range, I would suggest one of the FM systems.