Alright m8 calm down
At the end of the day what does a car alarm do? It just goes beeeu weeeeee uuuur uuuuur when one of the sensors is activated. 99% of people will completely ignore it. Immobilisers are obviously essential as they will stop opportunist brain dead twokkers from stealing your car.
But there are gangs out there who if they see your car and want it will steal it whatever you do. Not all twokkers are thick, cars can be stolen to order by highly organised gangs. Ive heard of people getting followed home from car shows and having their cars lifted after people have scoped out what ICE they have in the boot. As for nobody wanting to nick a 172, well they are worth over 10 grand so they are a prime target for ringers.
I know if you have 4 grands worth of car stereo you might want the peace of mind of a top end alarm system but at the end of the day thats all it is, just peace of mind. You might deter the local smackhead from going at the car with a screwdriver but as with everything these days people can be organised and efficient if they are serious about what they do.
All Im trying to say is that even on a £600 clifford alarm system the most effective deterrant is the sticker.
Oh and Im a security engineer so I know a bit about security too