Alarm rattles building (7)
I believe the answer is:
startle
'alarm' is the definition.
(I've seen this before)
'rattles building' is the wordplay.
'building' is an anagram indicator.
'rattles' with letters rearranged gives 'STARTLE'.
(Other definitions for startle that I've seen before include "Cause shock to" , "Take unawares with rattles" , "Cause shock/alarm" , "Astonish" , "Alarm suddenly" .)