Setting the alarm off about nothing is unprincipled (6)
I believe the answer is:
amoral
'is unprincipled' is the definition.
(I've seen this before)
'setting the alarm off about' is the wordplay.
'setting' becomes 'o' (I can't explain this - if you can you should give a lot more credence to this answer).
'off' indicates anagramming the letters.
'about' is an insertion indicator.
'alarm' anagrammed gives 'amral'.
'o' inserted inside 'amral' is 'AMORAL'.
'nothing' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for amoral that I've seen before include "Ignoring ethical considerations" , "regardless of what's right or wrong" , "Without an ethical code" , "Unprincipled" , "Having no standards of right or wrong" .)