A moaner, but she has her charm (5)

I believe the answer is:

siren

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'charm' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I can't see?

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for siren that I've seen before include "Warning signal generator" , "Vamp; alarm" , "Seductress" , "Hooter - femme fatale" , "Bewitching singer,part- woman, part-bird" .)

I've seen this clue in the Evening Standard.

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