Eg, stopwatch (5)
I believe the answer is:
timer
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">eg stopwatch</span>' is the definition.<br/ ><span class="explanation-format__explanation">(stopwatch is a kind of timer)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for timer that I've seen before include "One may be alarmed" , "Clock, say" , "Preset mechanisation to activate a device" , "chronometer" , "Stopwatch, say" .)