The most common and most likely answer to this crossword clue is the 9 letter word CARABINER
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More clues leading to the result CARABINER
Buddy explains!
The straight part
We know that "safety device" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case safety device = carabiner.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 CARABINER mean?
CARABINER noun- A metal link with a gate that can open and close, generally used for clipping ropes to anchors or other objects.