Crossword Genius

When one’s ticker stops, one expires (9)

Ross

I believe the answer is:

stopwatch

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But I can't explain it at all! Could you help me understand?

(Other definitions for stopwatch that I've seen before include "Timepiece for exact timing" , "Timing device, for sports perhaps" , "Race timer" , "Timepiece for recording speed of racers" , "Timepiece for timing, a race perhaps" .)

I've seen this clue in The Hindu.
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