Actually, when those motion sensors are installed properly, in areas which have frequent down-time like office spaces, they save so much money that they literally pay for themselves in under a year, and all of the savings after that are net. They last a long time and require almost no maintenance beyond occasionally adjusting the direction of the sensor if the space's furniture or partitioning is re-arranged.

Installing them in a checkpoint queue, however, doesn't seem optimal to me. It's a spot that has traffic all day long, and in a few airports, 24/7.

My gut tells me that the things redii saw in HOU are radiation detectors, though. Seriously. It would be just like TSA to spend money on a practically non-existent threat vector, as they already do with liquids and small knives and drug interdiction.