The most common and most likely answer to this crossword clue is the 4 plus 4 letter word CAPS LOCK
I've seen this crossword clue in The Guardian
C
A
P
S
L
O
C
K
More clues leading to the result CAPS LOCK
Buddy explains!

The straight part
We know that "key" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case key = caps lock.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.