There is already a SCOTUS ruling on this issue: Kyllo v. United States (http://en.wikipedia.org/wiki/Kyllo_v._United_States)
In this case, the police used FLIR (Forward Looking Infra Red) cameras equipped on a police helicopter to look at the heat signatures through the walls of a house.
The courts ruled (5-4) that doing such is a defacto search of the property and a clear 4th amendment violation.
The point of the ruling, is not the intrusiveness or the technical means by which the police overcome the privacy and property rights, but the fact that doing so is a search of the property.
Justice Scalia, who wrote the presiding opinion, further went on to protect against all future attempts at bypassing the barriers of privacy and conduct searches of property without a warrant by the way he wrote his opinion. Again, it is not the technological means by which one overcomes the property's barriers to privacy, regardless how non-intrusive or passive such measures are, but the fact hat doing such is conducting a search of the property.