i've got 1 alarm, shock sensors, ultrasonic sensors, 3 immobs, reinforced security window tints ....... and largely nothing worth stealing in the car, no stereo or speakers.
like everyone has said, if they want to get in, they will - it doesnt make any odds what security you have. i used to bolt my stereo down at the back using 3mm steel cable to the firewall, but it just meant, they'd never be able to remove it and just damage the crap out of the dash to try and get it.