With which to sound alarm or ring the changes (6)
I believe the answer is:
hooter
'with which to sound alarm' is the definition.
I can't judge whether this defines the answer.
'or ring the changes' is the wordplay.
'ring' becomes 'O' (letter resembling a ring).
'changes' indicates an anagram.
'or'+'o'+'the'='orothe'
'orothe' with letters rearranged gives 'HOOTER'.
Can you help me to learn more?
(Other definitions for hooter that I've seen before include "it smells" , "Factory siren" , "Siren, horn; nose" , "Car horn or slang nose" , "Gnomon" .)