A magic eye, perhaps, for rating film by the sound of it (6)

I believe the answer is:

sensor

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'a magic eye perhaps' is the definition.
(I know that electric eye is a type of sensor)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for sensor that I've seen before include "Device that reacts to stimulus from snores" , "A furtive look" , "One detects" , "that could provide a smokescreen" , "device to detect change?" .)

I've seen this clue in The Irish Times.

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