remember that RF signals act differently than other electrical signals. although connecting the antenna to the body of the car may create a larger surface area for the signals to be routed through keep in mind that for the most part you are changing the antennas physical makeup which may just screw it all to ****....not to mention the body is probably going to be at ground anyways so it wont work at all. routing it near a window is a much better idea. extending the length of the antenna, not the area, is a decent idea. for the low frequency signals that car alarms use extending your antenna length will probably work pretty well.