TEMPEST doesn't specify that the transient signals are transmitted through any particular medium. A. Are there transient electromagnetic signals that are leaking information? B. If so, someone gathering and analyzing those signals is engaged in a TEMPEST attack Honestly I just glanced at the paper, maybe you are right, but it seemed like they were working with electromagnetic emissions, if it were only power consumption data being used then it wouldn't be TEMPEST but this doesn't seem to be the case from my quick scan of that paper.