proximity alarm

I just want to know what is the best place to put my module for the proximity detection (2 zone, inside and outside the car), it says that is must be most possible in the middle of the car, so I was thinking about the compartment for the handbrake, hidden, is it a good place? or any other suggestion??

thx a lot!

I was considering that location as well, one installer recommended underneath the rear seats as the best location.