The car body as a Faraday cage works if you drive a big peice of Detroit steel with a metal body, rather than the plastic ones so in vogue now, and you have a ground wire hanging down for your radio. And if you have a car old enough for good metal body panels, you probably have fuel injectors. But odds are, if it's taking out pacemakers, it's gonna get your fuel injector no matter what your car is made of. And since cars aren't generally grounded, the energy will probably try to go to the terminal in your battery, and break things along the way.

And you're right, I should have pointed out that all an antenna is is a piece of wire. I forget that it isn't common knowledge.