Well, I don't know if it work or not, but was planning on putting a set of Double A or something into the trunk for the alarm. Since most thieves be going straight to the main battery to stop the alarm. Wouldn't it be great after they disconnect that and your alarm is still going with another battery?

 

The alarm will need 12V, it uses very little power when just armed, but when it goes off it can use 2 or 3 amps just for the siren, and if park lights are wired a lot more.
A much better way would be a back-up batt. siren, it can be wired completely independent of the alarm, and even if the alarm was not armed, if the car batt. is disconnected it will trigger, in fact you could rip it out of the car and it still would keep making noise. 94