There are many alarm systems that are extremely sophisticated to
protect your car to a huge extent but they will cost you a
lot.
for example, a viper system with cameras and recording and
proximity alarm as well as a 2 way key will set u back by thousands
of dollars.
however, the cameras (if lets say you put 4 or 5 cameras) will
record any incident to your car, including scratching keying,
etc.
proximity alarm will also detect anything coming close to your car
(doesn't work for normal carparks where cars are parked side by
side) and stages allow the alarm to vary according to stage.. when
someone is approaching ur car it could give a friendly warning, if
thye come closer, the alarm could sound, then if they touch ur car
then the alarm will go crazy etc.
the alarm can also be made to call the owner so the owner can
immediately attend to his car.
cameras will also record anyone who does anything to your car
unless he/she wears a mask.
hmm so ya..
however, the best is to hire security guards to guard ur car round
the clock