The thing is, they need a warrant to search your home *before* they use thermal imaging on it. And, if they have a warrant to search your home, they won't bother with thermal imaging; they'll just pull up with a few squad cars, knock your door down, and tear your place apart. That's much cheaper, more effective, and undoubtedly more fun than thermal imaging. The Supreme Court already ruled on this in the U.S. -- warrant first, then thermal imaging. Not thermal imaging, then warrant. As long as you give them no reason to get a warrant, you have no need to fear thermal imaging.