well, i think the basic steering lock and also the gear lock works. Also, hide the alarm reset button for ur car as it is easy to hot wire ur car and reset the alarm if the switch is not hidden coz everyone knows where the alarm switch is.
Also for just a few ringgit you can add in a starter kill switch for it, kinda like a ON-OFF button for the main power of the car.
Get sensors like motion and shock sensors costing about RM100 each. CHeck out ebay for Viper sensors which are selling relatively cheaper there than in Malaysia. In Malaysia, the motion sensor for Viper sells for RM300, i bought mine at RM120 on ebay with courier.
Also, I bought my Viper 791XV 2 way alarm with remote start from US imported to M'sia for RM900, whereas it would cost RM2,700 (with installation) if u buy it here.
I believe that a Electronic Light (EL) display for Viper also helps deter car thieves as it makes the thieves think u have a sophisticated alarm system. The EL display cost only RM100 and it just works as a light flasher but it kinda gives the psychological effect to deter thieves.
Buy only HU that have detachable face plates.