I went through SLC on Sunday and DEN in Tuesday and only some of the machines were being used at both airports. Naturally, I got in the line that had the NudiScope roped off. At least in DEN the machine that was not in use was functional because as I exited a PAX was in it. At SLC I noticed a large number of people alarming the WTMD and they were being sent to the penalty box and were being given a cursory pat down.

At both airports the lines were not that backed up and at least at SLC the original TSA == Thousands Standing Around was quite appropriate. Much to my amazement.

My personal observation is that perhaps the TSA is selectively not using the NudiScopes so that those who really object can find a line that they can use to pass through unmolested while those who meet a criteria are being sent through in an abundance of caution. For those who do not care they get in any line they want.