Thanks for the photos, CavePearl.

They're too far away from the equipment to be dosimeters*; you'd want to measure energy from the x-ray machine at a similar distance/orientation to where a human would be standing, not several feet up in the air.

*Of course there's every possibility that the brain trust at TSA has gotten this wrong.

My first thought is that they may simply be downward-pointing cameras for standard security (in the old-fashioned, pre-9/11, who-took-my-laptop sense) coverage. I don't know HOU but it appears from the photos that the checkpoint is in an atrium and the ceiling directly above it may be too high for surveillance cameras to get a good image. It also seems like the placement is where you'd want to monitor for petty theft (near the x-ray rollers) or aggressive behavior (in front of the NoS ).

That would be pretty boring. I'll try to come up with a more controversial theory.