Nervously try fire alarm a lot (7)
I believe the answer is:
terrify
'alarm a lot' is the definition.
(to terrify someone is to seriously alarm them)
'nervously try fire' is the wordplay.
'nervously' indicates anagramming the letters.
'try'+'fire'='tryfire'
'tryfire' is an anagram of 'TERRIFY'.
(Other definitions for terrify that I've seen before include "Fill with fear" , "Frighten badly" , "Scare badly" , "Fill with dread" , "Greatly frighten" .)