If you're in the U.S., they can't thermally image your home without a warrant, because thermally imaging your home IN AND OF ITSELF constitutes a search. Thermally imaging your home without a warrant is a violation of your 4th amendment rights. The Supreme Court has already ruled on this, and it's the law of the land, in all states. And, if they have a warrant, they won't need to thermally image your home at all: easier and cheaper to just send two or three squad cars and tear your home apart. The key is avoiding any reason they can use to get a warrant (smell, paraphernalia in sight, leaves in your trash, whatever).