Secret listening devices (4)
I believe the answer is:
bugs
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">secret listening devices</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 bugs that I've seen before include "Insects or defects in computer programs" , "Small crawling creatures or disease-germs" , "taps" , "Secret listening devices" , "Creepy-crawlies in computers" .)