Alarm if I become known (8)
I believe the answer is:
familiar
'known' is the definition.
('familiar' can be similar in meaning to 'known')
'alarm if i become' is the wordplay.
'become' indicates an anagram.
'alarm'+'if'+'i'='alarmifi'
'alarmifi' anagrammed gives 'FAMILIAR'.
(Other definitions for familiar that I've seen before include "Conversant with the witch's cat?" , "Usual; well known" , "Well-known witch's cat" , "Intimate" , "Well known like witch's servant" .)