I took a look at my service manual. There are 3 wires that run between the "security control module" and the "keyless entry control module." They were pink, light green with black, and red with white. One of those probably disarms the security system, you'll have to look at it with a meter, and try manually triggering it. The alarm you buy should have a factory alarm disarm output.
Or, you could just unplug the security control module.
Download the manual for your car on the link up there, open the wiring diagram, and search for security.