The precursors are a nitric/sulfuric acid mix and glycerin. I believe that the puffers would detect some fumes off of the concentrated acid but we all realize that the puffers are seldom used. The glycerin is unlikely to be detected as so many products (e.g. soaps) would cause false positives.

My understanding is that producing it does not require very controlled conditions - other than temperature (and the big issue here is to keep the product cool enough so it doesn't go off prematurely - which is likely only to concern a terrorist insofar as if it occurs before enough product has been produced to guaranty the destruction of the aircraft - an further, it doesn't strike me as a major engineering feat to construct an ice bath for cooling).

And if even this is considered too unlikely, how about a terrorist that wears clothes made of nitrocellulose onto the flight?

My point is that there are real threats, but the TSA is failing to protect us from them while inflicting their own damage upon the traveling public.