How is a drug sniffing dog more intrusive than a full-body scanner? The test of whether technology is a search for 4th Amendment purposes has generally been whether that technology does something a law enforcement officer could do without a warrant. E.g. a GPS tracking device attached to a car or package is OK, because the police could follow the car without a warrant – it just saves the police time to attach a GPS tracker. But a heat-imaging sensor detecting extreme energy usage and warmth in a house (for purposes of finding out whether someone was growing marijuana w/heat lamps) was found not to be OK, because it gave the police a look “inside” the house that they wouldn’t have been able to get by themselves, unless they got a search warrant.
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Wow, that’s interesting. It seems that, historically, our culture has found that an unwarrented intrusion into the privacy of a person’s home cannot be justified by the probability that it might prevent crime and make us safer.