What's this? (Roll-up Garage Door Content)

We've been house hunting since the spring and finally found the one. The inspection was today and went well. One thing that came up was this guy that's coming from the roll-up garage door for the fenced parking pad. It's clearly got some sort of tension cable that runs in a long (10'?) compression housing (like bike cable housing) to this guy in the pic. seems like an adjuster of some sort. neither me, the very good inspector (deal killer kind), or our good friend the architect/developer knew what it was for. So of course one of you guys do

it's coming from something like one of these:

In reply to bluej:

First pic isn't working. The url looks a bit knackered.

In reply to petegossett:

Blarg. Thanks. Fixed, I think. Stupid google photos

It probably has a torsion spring, like most garage doors but inside a housing that rolls up the door instead of on tracks.

But what does that have to do w/ the black twist knob in the pic?

Is the coiled black cable part of it? If so, it looks electrical. Maybe an alarm or doorbell of sorts?

Where does the other end go? Is the bare cable end anchored inside the black section?

Interesting timing. I have two wooden crates in my yard with a steel roll door just like that in them. I didn't unpack it yet but I do not recall seeing a cable actuated anything in the ordering process. Mine adjusts with the tried and true wound spring of terror and a crowbar method.

I'll be installing it sometime after work tomorrow and I'll make a note if I see anything of that sort.

I'm going to throw out a wild ass guess.

It's the adjuster for the braking system.

Figured out how to get the image address from the listing. Here's the setup:

ENHANCE version:

Detail pic again:

So the doohickey knob is a termination for the grey wire tension cable coming out of the top of it (detail pic). The black cable coming out of the bottom is the combo of the tension cable and it's housing (think bike cables/housing). The tension cable/housing is wrapped around the control box on the adjacent wood fence. I can't recall exactly if the tension cable/housing terminates in the control box, or up in the housing for the roll-up door.

Basically, I know it's a knob for adjusting the tension in the cable vs. the compression housing. What I don't understand is exactly what that is in turn doing as related to the roll up door..

The tightly coiled wire in the background of the detail pic runs to the bottom of the roll up door and is the signal carrier for the stop sensor.

Cable actuated lock for the door?

I'm changing my wild ass guess.

It's the motor release, for a powered door. If the power goes down, that cable will disengage the motor from the door, so you can raise the door manually.

I'm taking notes. whoever gets it right gets a cookie. well, and a beer next time they're in DC