The most common and most likely answer to this crossword clue is the 8 letter word TWO-TONE
I've seen this crossword clue in The Guardian
T
W
O
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T
O
N
E
More clues leading to the result TWO-TONE
Buddy explains!
The straight part
We know that "sounding like a siren" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sounding like a siren = two-tone.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 TWO-TONE mean?
TWO-TONE adjective- Having two colours or shades.
- Giving two different sounds, either alternately or simultaneously.