Best one for that is the Clifford 500 mate!!
Spec:- Has its own battery incase sum1 cuts car 1.
A key pad which you put a code into so that even if sum gets ur keys they cant seal ur car!
A sensor that detects wen sum1s snoopin asround ya car and then chirps at them as a warnin The only way they cud nick ur car wud b to toe it!!
There r other things u can add later on as extras, eg, auto window wind up, boot release, auto engine start plus more. Though wen u take it it to have work on it u'l need to turn alot of the features off temperarily.
I highly recommend this alarm.
Deano