Anything above 0Hz radiates. EMF is short for 'electromagnetic field' which even DC produces, so I guess I could have worded it better.
In any case, I would want to detect the emissions from the CPU, memory bus and SD card traffic. Not all cameras are WiFi. Sure, that won't detect passive listening devices or other advanced techniques, but most people now are worried about video and that will have certain characteristic emissions.
Isn't that effectively all the EMF? You may be missing a prefix.
Edit: huh, turns out these frequencies do have some applications: https://en.wikipedia.org/wiki/Super_low_frequency