The second of the court’s new dog cases asks if the police may take a drug-sniffing dog to the front porch of a home to sniff for evidence of marijuana inside. The court has always accorded special privacy protection for people’s homes. In 2001, the court ruled, in an opinion written by Justice Antonin Scalia, that police officers violated a homeowner’s privacy when they parked across the street from a home and, without a warrant, used a thermal imaging device to scan the outside of the house for signs of unusual heat inside that might be caused by high-intensity lighting, which is often used to grow marijuana.

If the police can’t thermal-scan your home from the street, why let them dog-scan it from your front porch? The government argues that a dog is alerted only by illegal contraband, while a thermal imager is set off more generally by “innocent” and “guilty” heat of all kinds coming from a home — whether from grow lights or from, as Justice Scalia noted in the thermal imager case, “the lady of the house” as she “takes her daily sauna and bath.”

But, arguably, this distinction is misplaced. If the court rules for the government in the home-sniff case, it is hard to see why the police could not station drug-sniffing dogs outside the entrances to every school, supermarket and movie theater as a routine form of drug interdiction. Dog sniffs would never involve a privacy intrusion and therefore would not trigger the requirement that the police obtain a warrant or have individual suspicion.

Moreover, today’s dogs will give way to tomorrow’s high-tech contraband-scanning devices that, under the reasoning pressed in the dog cases, would free the government to conduct routine scans of people’s homes or their bodies for all manner of contraband (or possibly for noncontraband, like marijuana grow lights, that are most commonly associated with illegality).