Sex, Drugs, and Fourth Amendment

Prof. Orin Kerr, over at Volokh writes the following regarding a 4th amendment case involving government swabing door knobs to test for traces of drugs. I'm not familiar with the case so I can't go into the details, but based on Kerr's analysis it's mostly seen as a seizure issue. I'm wondering why it's not a search issue within the SCOTUS's decision in Kyllo . Scalia wrote for the majority:

We think that obtaining by sense-enhancing technology any information regarding the interior of the home that could not otherwise have been obtained without physical "intrusion into a constitutionally protected area," Silverman, 365 U.S. at 512, constitutes a search -- at least where (as here) the technology in question is not in general public use.

Well the physical intrustion is there, the question is if the area is "constitutionally protected." Then this depends on what society expects to be protected. Ironically, Kyllo used heat lamps to grow pot in his attic, hence the thermal imaging. (Maybe they should have swiped his door knob).