If a device that was capable of smelling marijuana from miles away existed and was very accurate (could identify houses where the smell was coming from), would police legally be able to use it for the detection of marijuana in a neighborhood?

  • 1
    In what country? In what State (if US)?
    – Ron Beyer
    Apr 2 '20 at 22:29
  • I didn't realize it would vary by state. I am mostly interested in the US, although various countries are interesting nonetheless (it's cool to know). I suppose what are a couple examples? I would say non-marijuana states as it makes more sense that way.
    – JVE999
    Apr 2 '20 at 22:34
  • I don't see why they wouldn't be able to legally use that against you. They can use drug-sniffing dogs on vehicles without a search warrant (but they need to get one to enter your property, and the dog/device gives "reasonable suspicion").
    – Ron Beyer
    Apr 2 '20 at 23:04
  • While the 4th Amendment principles don't vary by state, the application would vary greatly by state and over time. For example, hemp production is now legal nationally in the U.S. and indistinguishable in smell from marijuana, so a distant marijuana smell would not provide probable cause that a crime was committed. One or two cases at least have been decided on that basis. There is also a fair amount of law as to what tech counts as a warrant requiring search. A supersniffer probably would.
    – ohwilleke
    Apr 2 '20 at 23:37

The relevant case is Kyllo v. US, 533 U.S. 27, where heat emanating from inside the house was detected remotely (without entering the house). The primary question is whether in that case a "search" has occurred. Relying on Katz v. US, 389 U. S. 347 (where sound wave were picked up from outside a telephone booth), there is no search unless the individual manifests a subjective expectation of privacy in the searched object, and society is willing to recognize that expectation as reasonable. "Obtaining by sense-enhancing technology any information regarding the home's interior that could not otherwise have been obtained without physical 'intrusion into a constitutionally protected area' constitutes a search – at least where (as here) the technology in question is not in general public use". In other words, a "search" is not defined in terms of entry into a structure, it is defined in terms of a socially-recognized reasonable expectation of privacy. Accordingly, this magic device conducts searches, which means that a warrant is required.

  • I just found Kyllo has a website with some relevant and interesting links.
    – JVE999
    Apr 3 '20 at 13:55

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