2 shock sensors

Would I benefit from having 2 shock sensors, 1 for the front and one for the back?

What about for a car? I have my shock sensor mounted up under the driver side of the dash. The sensor works great for the middle to the front of the car, but isnt as great for the rear. I was thinking of mounting another shock sensor somewhere in the trunk to take care of the back end of the car and then simply tie that trigger wire into the front sensor's trigger wire. Also, would it be better (safer) for me to run the power wire for that sensor (and maybe even the ground wire) up to the front of the car, then ground the ground to the chassis and run the power wire to another power wire from my alarm (not the other sensors power wire)?

Would I benifit from having 2 sirens sounding instead of 1?