Pager (6)
I believe the answer is:
beeper
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">pager</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 beeper that I've seen before include "electronic device" , "Emitter of electronic sound" , "pager, perhaps" , "pager, eg" , "Electronic alarm" .)