a 200 dollar viper is not much better than stock alarm. if you just want to spend a minimal amount of money on the shock sensor and think that now ur car is safer, you are wrong. a thief can break into ur car without triggering the shock sensor or the factory alarm. if i was you, i would either replace the factory alarm with an aftermarket one that has all the features or save the money. a shock sensor only costs 10 bucks maximum but the labor..at least 50. bottom line, don't be cheap on a security system. i don't hope to see you going through what i've experienced. i don't think you would wanna know what happened