More of a sigint and electronics thing. I know more theory than practice, though.
Radio and microwave circuitry basically deals with the fact that even a straight piece of wire has both a capacitance and inductance (albeit, very low). If I have a long enough wire and I "turn it on" - even without it being connected to the the "other side" - just like how current flows into a capacitor without a path to ground, it will flow into a wire. Get to turning it on and off really fast, and you can drive power into a wire that has no complete circuit - itself behaving like an analog tank circuit (LC resonator). Things get a bit weird with geometry, here, as propagation is not in one dimension or two, but three… which is how waveguides and other fun things work (even antennas… to be honest, there still isn't a really good explanation for antennas … consider, is there a photon exchanged between coils of a transformer - how are these photons radiated and the distincion made between coupled coils and antennas?).
There's a lot more room here for discovery and innovation than many realize, I think. Fewer particle accelerators, more bulk materials and transmission research.
Old coax was pretty simple and is just a microwave transmission line. Modern lan cable is several microwave modems on each line. Modern wifi is even higher frequency microwave with multiple antennas used for additional bandwidth.
In principle, most of the data bus lines in a computer are microwave stripline. They could be read… or, perhaps more accurately, detected. Reading implies getting something intelligible out of them. It might be possible to read individual bus lines from a distance, but that would be at the edge of physics as you'd need to use some crazy means to differentiate between them… like computing the phase angle between a few photons type stuff… which could probably be done in a lab, but might be difficult to realize for anything practical.