You have to have a program running on the computer under attack for this to work, because it has to execute specific instruction patterns. It can only send blind; it can't receive. The main situation in which this would be useful is when attack software has been placed on a laptop, then used by then target.

RF attacks on serial connections (which includes not just serial ports but USB and Ethernet) are much easier. All the bits you want are right there. Historically, Teletypes generated RF which was easy to monitor, and the Friden Flexowriter could be monitored from half a mile away.