Method of echolocation (5)
I believe the answer is:
sonar
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">method of echolocation</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for sonar that I've seen before include "Underwater detection system" , "Echo-sounding device" , "Detection system at sea" , "Method of echolocation" , "Undersea sensing system" .)