The trespass rationale worries Christopher Slobogin, who directs the Criminal Justice Program at Vanderbilt Law School. "If the next case involves a drug-sniffing dog smelling an apartment that abuts a public sidewalk, presumably Scalia would say there is no search because there is no trespass," he says. "But the privacy invasion of the home would still be just as significant." Plenty of urban residences are within a few feet of a sidewalk, making them vulnerable to an accusatory Labrador retriever.
Justice Elena Kagan agreed, in a concurring opinion. In her view, cops violate privacy rights "when they use trained canine assistants to reveal within the confines of the home what they could not otherwise have found there" -- even if they do it from a public way.
Why does it matter? Because dogs are the least of the ways in which the government will eventually be able to monitor spaces that once afforded sanctuary to anyone who wants to be left the hell alone. Last year, the court said police needed a warrant to put a GPS tracking device on a man's car because they "physically occupied private property" -- the vehicle -- "for the purpose of obtaining information."
But the day is nigh when the government can use a tiny drone to follow a car day after day. That would not require a cop to put hands on someone's personal property. But the information gathered would be no different. It's hard to see why one would be barred by the Fourth Amendment and the other would not.
Even Scalia may grasp that. In the GPS case, he acknowledged, "It may be that achieving the same result through electronic means, without an accompanying trespass, is an unconstitutional invasion of privacy." Still: May be?
A person's right to keep others off his property was once a sturdy protection for privacy. But in an age of intrusive new surveillance tools, it could leave us all with nowhere to hide.