Tools: philips screw driver, 10mm socket and ratchet.
* shock sensor ($15). you can get it from Best Buy ($40) or local car stereo/alarm shops (cheaper).
* Female prong (connector). you can get it from AutoZone, Radio shack for about $2-$3/dozen.

Time: 1 hr (max).

Difficulty: (1-10) 5

First you need to remove marked screw and bolt in the below picture. Then pull the under dash piece down to remove it.

Unplug all the front harnesses (You'll need to reset your seat position memory when you're done). Push the fuse/relay box toward the passenger side, turn it side way and pull it out little so you can see the marked harness. This is the hardest part.

On the shock sensor, there are 3 wires (instant trigger) or 4 wires (dual-stage trigger). Connect the black wire (sensor) to the black wire (harness) and green wire (green/blue for dual-stage) (sensor) to yellow wire (harness). Put the fuse/relay box back to its original position. NOTE: I didn't mention the silver dots since every wire in the car has silver dots on them.

Connect the female prong to the end of the red wire. then connect it to the second for the left empty harness on the bottom row on the back side of the fuse/relay box as in the pic. The slot is marked "U"

Find a place not to sturdy to mount your shock sensor. I placed it in the wire mess below the fuse box on the side that faces the fuse box cover. NOTE: if you secure the sensor on a hard surface, it would take a very hard impact to trigger the sensor.

Arm the alarm, wait 30sec (the HELM manual states the system arms immediately but not in my case) then hit the glass (do not break it) it should trigger the factory alarm. Adjust the sensitivity to your liking. When you finish, place the under dash piece back, put the screw and the bolt back. DONE.

Good luck.