Last Thursday I posted about new explosive detection machines costing $3 Million each.  Here is an article saying they cost only $130K to $150K each.  A much more reasonable price to pay.  I don’t know which is correct but it really doesn’t matter all that much because the most interesting portion of the article is this:

Sniffers are proving to be very sensitive, said Deirdre O’Sullivan, a spokeswoman for the TSA, sometimes indicating “hits” for persons who might have had contact with substances such as fertilizers, which can be used to make explosives.

So far, she said, sniffers haven’t uncovered anyone of interest or suspicion to law enforcement officials. Still, terrorists have lots of weapons that worry the air travel industry and law enforcement agencies. Shoulder-mounted rockets, for example.

This is the problem… The number of false positives far exceeds the number of valid detections and will always be the case.  If the alarm threshold is adjusted such that a reasonable number of false positives are experienced (say 1%) then a well scrubbed explosive device will pass.  If the threshold is set such that nearly any amount of care in explosive device preparation will be caught then the majority of innocent people will be subject to additional searches.  Because of the high cost (time of the screeners as well as the complaints of the innocent) and predominance of hits being false positives (100% so far) the threshold will be adjusted such that the well scrubbed device will pass without detection.  And this scenario doesn’t even include active opponents working against the machines in the days to weeks ahead of the attempt to get an explosive device past the machines.

Hence the explosive detection machines do nothing but provide comfort for those with mental problems (denial in this case) and actually make things less secure because that same money could have been spent on effective security.