best place to mount shock sensor?

Ok, so how much "experience" credit do you give Directed Electronics, Inc. ?

THEY are the ones who make this recommendation.

So, I guess on THAT note, it's my $200 million 

This forum is full of so many big headed, self righteous installers it's almost shocking.

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Here are some links partially for your reading pleasure, but more so to dispell your ignorance:

http://www.crutchfieldadvisor.com/ISEO-rgbtcspd/learningcenter/car/security_install.html

Quote from above link: "Attach shock sensors solidly to a metal surface, using screws. Try to take advantage of an existing screw in your vehicle. If you can't find a good one, you'll have to supply your own screw. As an alternative, you can strap the shock sensor down, using nylon wire ties. Do not use Velcro or tape. "

http://www.commandoalarms.com/installtips.html

Quote from above link: "Find a location for the shock sensor that is close to the control module so the wire will not have to be extended. Keep the sensor away from heat sources. Mounting the shock sensor to the steering column (making sure not to interfere with the steering functionality) or tie wrap the sensor to the alarm wiring harness bundle for added sensitivity."

Ahhhh.... the wiring harness will wiggle and shake, setting off the trigger. Good point. I where DEI and my new crimestopper alarm said use the harness. Thought they were insane.

Have my CS sensor mounted to the firewall and I'm not that impressed. Will relocate to the fat harness....

The point that you're failing to see if that malicious shock will likely come from outside the car, which shock has to "shake" (if you will) the "piece with a higher density" as you put it, in order to shake that same "fat wiring harness".  As the vibration travels through more objects, it is going to gradually be absorbed and there will be less vibration to trigger the alarm once the it reaches the sensor.

As an example, say some one kicks a big dent in your drivers door.  That "malicious shock" (for lack of better term) will travel through the sheet metal of the door to the hinges in front and the locking mechanism in back into the body/frame of the vehicle.  From there will shake the firewall and may perhaps the wiring harnesses at some point.

I don't think that any one would argue that the wiring harness, not being a solid structure WILL absorb, to some degree, an amount of the shock or vibration, which DECREASES sensitivity.  That also is simple physics.  If the shock is going to travel THROUGH the frame/body of the car to GET TO a wiring harness, you're going to get the most sensitivity by mounting the shock sensor earlier in the vibration chain (if you will) so that the shock sensor picks up the shock before it has travelled through MORE items that are going to absorb the shock.

Given this, if you mount that same shock sensor INSIDE THE DOOR that was maliciously kicked, that will give you the greatest amount of sensitivity.  Since most cars only have a single shock sensor, most 'professional' installers recommend mounting the sensor central so that it will evenly 'sense' shock from any part of the vehicle (front, back, etc.)  However, doing this, you are RELYING on the fact that if someone rear ends your car in a parking lot that the vibration is going to travel through several components (all of which will absorb some of the shock) and still have ENOUGH "shock" left over to set off the sensor to notify the alarm to go off.

The bottom line and FACT of the matter is that by mounting a shock sensor on the wiring harness, you're placing the sensor "farther down in the food chain" so to speak, as opposed to mounting the shock sensor to the body/frame of the vehicle, which you're relying on to "transfer" the shock anyway.

Suit yourselves... where ever you mount your shock sensors, thoroughly test them to make sure that they are sensitive to your satisfaction.   All I can tell you is that if you mount the sensor ON THE FRAME/BODY/FIREWALL, your sensor will be "closer" to the SOURCE of the shock and therefore will receive more vibration, making it (in theory) MORE senitive.  At that point, you can decrease your adjustment on the sensor to fine tune the degree of sensitivity that you want.

This is the FACT of the matter, friends!

I also agree with Bret-

  A shock sensor picks up vibration,   not movement.    The frame of the vehicle will have way more vibration than any wire harness in a car.         If you want false triggers when its windy then by all means zip tie that sucker to a wire harness because it will be moving along with the car.   

To each his own.    Do whatever you think is best.     But it seems if you get back to basics youll probably find good sense in why its better to mount to a solid part of the car. 

I'll tell you what... to keep an open mind, I'll mount mine to a large wire bundle and do some theoretic testing to see if it seems that the sensor is more sensitive.  I do think that I'll likely mount it back to the firewall under the dash, but I have no problem admitting if I'm wrong and will certainly keep the sensor wired to the harness if it seems that it's more sensitive there.

I just think that simple physics tells me that mounting to the body (or frame, even better) is going to give you the most even sensitivity throughout the whole car.  I don't see how it can be disputed that a wire harness, no matter how big, will absorb some of the vibration.  I'll post results later next week when I get around to this.   :)