[Sir_Substance]

But consider:

Your house is constantly saturated with radio waves from TV stations, radio stations, wifi etc.

What if I were to design a device that passively received reflections of these signals rather then generating it's own to achieve the same function as the device in this post.

So I now have the same result, but I am "merely" receiving reflections, rather then making my own.

There is no difference in the function, this is rules lawyering at its best.

I am willing to let police observe emissions on visible wavelengths ONLY because that is a slippery slope to not being allowed to look into windows.

Anything you need a device to view is not ok to view without a warrant, no matter the technique.

[zaroth]

If you look at Gizmo's quotes, I think it's pretty clear they considered these kinds of technology tricks in deciding Kyllo, and 'taking the long view' that high tech collection of passively emitted information requires a warrant. I think the general approach is it's the result that matters, not the specific approach, e.g. 'expectation of privacy'.