Mad hatters' warnings (7)
I believe the answer is:
threats
'warnings' is the definition.
(threat is a kind of warning)
'mad hatters'' is the wordplay.
'mad' is an anagram indicator.
'hatters' is an anagram of 'THREATS'.
(Other definitions for threats that I've seen before include "Terrifying demands" , "Menacing statements" , "Statements of intentions to harm" , "Sources of danger -- shatter (anag)" , "Shatter (anag) - menaces" .)