Warned treadle is faulty (7)
I believe the answer is:
alerted
'warned' is the definition.
(alerting is a kind of warning)
'treadle is faulty' is the wordplay.
'is faulty' is an anagram indicator.
'treadle' is an anagram of 'ALERTED'.
(Other definitions for alerted that I've seen before include "Warned or aroused to a sense of danger" , "Put on guard, warned" , "Put on guard, raised the alarm" , "Put on guard, forewarned" , "Given signal" .)