By the way, it seems that Fel made a very common mistake/misconception concerning concept of energy, namely that energy is something physical, tangible. Energy is just possibility of doing work (or generating heat); it does not generate any kind of radiation. Example: how can you tell from afar if condenser is charged, battery is not dead, or mechanical clock/toy is winded up?They had two modes, passive and active, much like the old sonar used by ships and submarines.
Passive was listening for certain energy signatures, and active was bouncing a signal off an area to check for the specific pattern of the return. How the signal was returned would tell them the physical makeup of the material in question, and those were rather sensitive. Maya had him hide the skimmer under the bride to protect it against that sensor technique, while keeping it powered down protected it from the passive type.
Of course, it could just be misunderstood (on my part) simplification on Fel part... If it is, I'm sorry for my rant.