What is this, under my back seat??

[rcsoundn1]

come on OP we are waiting!

[reelizmpro]

i don't think it's a shock sensor, I pulled one out of my car, from under that dash you are correct, it had more wires hooking on the harness of the unit and little knobs to control the sensitivity of the device.

Looks like some kind of speaker to me?

Ooops, I meant to say Motion sensor which are supposed to be centrally located in the interior.