Late this past year the Supreme Court heard two cases related to the use of police dogs as drug detection equipment. It has long been established (United States v. Place, 462 U.S. 696 (1983)) that dogs could be used to check luggage for drugs at customs checkpoints and airports, and more recently (Illinois v. Caballes, 543 U.S. 405 (2005)) that an alert by such a dog outside a car on a legitimate routine traffic stop provides a reasonable basis for searching the vehicle. That was reaffirmed last month in Florida v. Harris; the more interesting case, Florida v. Jardines, challenges whether to expand this type of external searching to include homes.
The Fourth Amendment in the Bill of Rights protects Americans from "unreasonable searches and seizures", which means that the police cannot enter your home or office or other area in which you have a clear and reasonable expectation of privacy (it has included cardboard boxes in which homeless people live) and search for evidence of criminal activity absent some prior basis for believing that such evidence exists, sufficient to create "probable cause"--an articulable non-discriminatory basis for believing you might be involved in a crime which can persuade a judge to issue a warrant for deeper investigation. One of the most notable exceptions to this rule is the "plain sight exception", that is, if the police knock on your door because the neighbors are complaining about the noise, or to alert you to a manhunt for a dangerous prison escapee, or to collect for the Policemen's Benevolent Association, and they see something illegal when you open the door; or if standing on the street they hear a discussion of criminal acts through an open window; or if they smell an illegal substance outside the home; they have a probable cause basis for obtaining a warrant to search, or in some cases (exigent circumstances in which the suspect might destroy evidence) to enter immediately. There is an implied consent that any person, including a police officer, can knock on your front door, and thus can enter your property that far uninvited.
However, the Supreme Court is poised to decide whether this extends to his dog.
In oral arguments, the Court seemed unwilling to allow this. An officer who comes to your door with a trained drug-sniffing police dog may be conducting an illegal search, because there is no implied consent to allow a drug-sniffing dog onto the property. Thus a warrant based on the testimony that the dog reacted as if to the smell of drugs while on the suspect's property would be invalid; such detection methods exceed the "plain sight exception".
Although it applies specifically to dogs, it will also impact the use of technological surveillance. We live in an age in which thermal imaging can identify the locations and shapes of persons and of medium-heat equipment inside buildings; where flying drones can pass over a roof and detect concentrations of chemicals in the atmosphere; in which airplane and satellite imaging can view into fenced or walled yards; where laser sound detection can pick up conversations off the vibrations of glass in your windows. The ability to watch us, to put our most private rooms in the "plain sight" of investigating officers, has expanded beyond the science fiction imagination of placing cameras in our home televisions. We can be watched.
Fortunately, there are limits on such methods. That's not to say that they cannot be used; it says only that the police must already have probable cause. Kyllo v. United States, 533 U.S. 27 (2001), has already held that thermal imaging (specifically in that case to search for evidence of the use of heat lamps to support marijuana growth) is a search and cannot be performed without a warrant; last year in United States v. Jones, 565 US ___, 132 S.Ct. 945 (2012) the installation of a Global Positioning System (GPS) device on a car to track its movement for a month was ruled a search, requiring a warrant. The police cannot use more advanced technology to gather evidence about suspected criminal activity without first demonstrating that there is good reason to believe such evidence exists.
The present question, then, is whether they can bring a drug-sniffing dog onto your property without your consent unless they already have good articulable reason to believe that you are involved in drug crimes. It will be a significant step for our protections against search and seizure in an age in which privacy is becoming more and more difficult to protect from technological snooping; the question is in which direction.