The 4th ammendment is meant to protect you from the power imbalance with the government. Or at least that's how it seems to be interpreted by the courts. Kyllo

The 4th ammendment is meant to protect you from the power imbalance with the government. Or at least that's how it seems to be interpreted by the courts. Kyllo v. US ruled that heat-cameras mounted on helicopters were considered a "search" and could not be committed without a warrant because most people do not have heat-cameras and helicopters. But everyone has ears (and microphones obstensibly work as well as ears in public spaces). The government has the right to investigate on the same level as normal citizens, in a way. Binoculars are also fair game, because a lot of people have binoculars. The "expectation of privacy" is usually evaluated as "if somebody could try to spy on me, would they be able to do so relatively easily?" In a way, this 4th ammendment interpretation is what protects us from NSA mass-surveillance. Because only very few people have the resources necessary to set up such a network, you can end up with an expectation of privacy. And while you don't have an expectation of privacy with regards to tor nodes (anybody running a node could be trying to watch you), IIRC expectation of privacy comes in if , as in the recent case, the gov't runs a very large amounts of nodes and cross-references the data to "find" people.