OEM alarms... just about as effective as putting a sticker on your window saying "this vehical's owner owns a gun, nothing in this car is worth your life" ever seen that sticker? I have. Was it scary, or deturant? no. same thing with an OEM alarm.

check out some real alarms, that have more features like ignition kills, and anti bypass wiring.

I'll copy this to audio/electrionics forum, be sure to check for it in there.