Over the years, I've read about various shops marketing devices meant to protect drivers. The first that ever caught my attention was a company that installed electrified seats in the backs of cabs (in Europe, I think) back in the late 80's early 90's. One person was killed, charges were filed, arrests were made. In the years following Apartheid, I saw an add for a company that installed spring loaded blades under the rocker panels that could amputate a car jacker's legs. There was also a flame thrower feature. This was in response to the dramatic rise in jackings of luxury cars in SA.
http://transportation.frost.com/prod/servlet/market-insight-top.pag?docid=JSAA-5NCK62&ctxixpLink=FcmCtx25&ctxixpLabel=FcmCtx26.
Here in the States, I remember the introduction to the .410 shotgun shell revolver, designed to defend against car jackers back in the early to mid 90's. Crazy shit, eh?