Wake-up call (8)
I believe the answer is:
reveille
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">wake-up call</span>' is the definition.<br/ ><span class="explanation-format__explanation">(military wake-up call played on an instrument)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for reveille that I've seen before include "Signal to awaken soldiers at daybreak" , "Summons to get up" , "Military signal to wake up" , "Army waking signal" , "Soldiers' wakening call" .)