scanner on factory alarm

Hi guys, I have a question about wiring a LED Security Scanner to my 2004 VW Passat factory alarm. (http://www.amazon.com/Varad-VS350BL-Led-Scanner-Blue/dp/B000MISTLWFrom) The scanner has three wires: -Battery negative or chassis ground -Battery positive (constant) -Alarm system accessory output or ground output when armed. My factory alarm doesn't have a ground when armed output, as most factory alarms don't. I have been browsing the forums, and have seen you can wire latching relays to the door lock/unlock negative wires. If I understand right, I should use the "Latched On/Off Output Using Two Momentary Negative Pulses - Negative Output" diagram in order to create a ground when armed output. I would wire the lock impulse to turn on the alarm, and the unlock impulse to turn off the alarm. If I am correct, would me pressing the unlock button on my remote twice turn the relay back on? I am kind of new to relays so sorry if I butchered this layout/idea. Any input/better ideas would be greatly appreciated. md114l

Constant wire of the scanner to a constant 12V source. Connect the ground wire to the chassis.   Connect the ground when armed wire to an Ignition powered source. When you turn he key off, the ground when armed wire will see enough of a ground through the ignition system to think the alarm is armed and the scanner will illuminate.

Thanks for the reply, I appreciate it. That's kind of my last resort method right now. I really want the scanner to go on when I lock the car and off when I unlock the car.