While looking at the photos from this question
I noticed a small protrusion from the side of the plane. You can see it in the photo:
and in the diagram from l@aeroalias answer:
In the diagram it appears to have something to do with the apu or is fire protection system. There's a shaded line running to it.
What is this object?
Edit: It does look like an antenna. I found a diagram of 777 antenna placement here, but it doesn't show anything in that area.
APU Compartment Firewall,
Inlet Door, etc. $\endgroup$