Alerting light (5)
I believe the answer is:
flare
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">alerting light</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for flare that I've seen before include "Burst into sudden activity or anger" , "Warning light" , "(Burn with) sudden blaze" , "Spread" , "Distress signal; burst out angrily" .)