The most common and most likely answer to this crossword clue is the 11 letter word STETHOSCOPE
I've seen this crossword clue in The Guardian
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More clues leading to the result STETHOSCOPE
Buddy explains!
The straight part
We know that "a listening device" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a listening device = stethoscope.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does STETHOSCOPE mean?
STETHOSCOPE noun- A medical instrument used for listening to sounds produced within the body, often combined with a sphygmomanometer
- To auscultate, or examine, with a stethoscope.