In this case, enforcement doesn't matter quite so much -- if a heat scan counts as an illegal search, the evidence is inadmissable. Illegal searches happen all the time, and for most people there isn't much recourse. The fact that evidence gathered through illegal searches is generally not valid is usually enough to discourage illegal searches to the extent that the cops are more interested in building a case than they are in harassing you.
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But is it enforced?
Not sure what you mean by "enforced".
Do cops currently do thermal scans of random citizen's homes? Probably.
Can they go to a judge and say "the thermal scan says this house has a marijuana grow-op in it, give me a warrant"? No.
But they can file bogus paperwork saying an informant told an officer that the house has drugs in order to get a warrant.
In this case, enforcement doesn't matter quite so much -- if a heat scan counts as an illegal search, the evidence is inadmissable. Illegal searches happen all the time, and for most people there isn't much recourse. The fact that evidence gathered through illegal searches is generally not valid is usually enough to discourage illegal searches to the extent that the cops are more interested in building a case than they are in harassing you.