2004 sienna add shock sensor

I have a 2004 Sienna in the shop. 

It has the factory security system which of course does not have a proximity or shock sensor. I want to add a generic shock sensor to the vehicle to trigger the factory alarm.

I assume the best way to do this is to have the trigger output form the aftermarket shock sensor tapped into the door pin wire on the van? (of course diode isolated)

Is this the best way to add a sensor fucntiion?

THANKS 

As long as the windows don't drop a bit when the door is open it will be fine.  You also need to make sure the shock sensor is only powered with the ignition off, otherwise the dome light / door ajar will light each time you hit a bump.

You should also do a current draw on the door pin, I've seen door pins on newer cars (Infiniti G35 coupe to be exact) draw in excess of 1A to ground.  It fried the shock sensor the guy was trying to install, and he ended up going with the trunk pin.