Well "special hardware to detect EM radiation" is most often software-defined radios like HackRF or BladeRF among others down to TV reception dongles you can get for a few dollars (search for RTL-SDR)

I look forward to the day when SDRs are inside smartphones.

They probably already are just hidden behind closed source firmware

You usually need an antenna, yes. Does that matter?

It makes attacks much more limited. You need physical access to whatever machine you're attacking, versus being able to distribute code to millions of machines at once over the internet. That matters a ton.

it matters because if the hardware is difficult and expensive to obtain, an attack can be costly, and hence, won't affect the common man. Industrial espionage or state level espionage hardly changes for the common man, and since most of the hardware in use is by the common man, it's unlikely to get a real fix.

Effective antennas are reasonably easy to build from scratch (depending on the frequency band), and are commercially available in an insane number of variations. Either way is very cheap - as little as a few dollars.

Software defined radios can be had for as little as $10-20 for simple receive only types, up to several hundred for substantially nicer transceivers. They can also be $1000+ for special applications or R&D.

There are demos of things being done with RTL-SDR dongles which cost less than a good lunch.