What Is The Mystery Part Mounted Next To Rear Deck Speaker?

[Bardo's Pal]

In the trunk of my 97 ES300 there is a device mounted next to the rear deck speaker which has the following: DO NOT REMOVE, and underneath; C085407. It is cylindrical in shape and mounted in a black plastic holder. It doesn't appear to have any electrical connections that I can see. It also doesn't appear on the parts diagrams for the trunk or the luggage deck as it is called.

What is this thing and what is it for?

[austin_elliott45]

This is the seatbelt for the rear middle seat, its just all rolled up in the box in the trunk