Some rubbish about a safety device (6)
I believe the answer is:
refuse
'some rubbish' is the definition.
(refuse can mean rubbish or garbage)
'about a safety device' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'a safety device' becomes 'fuse' (electronic safety device).
're'+'fuse'='REFUSE'
(Other definitions for refuse that I've seen before include "Deny; rubbish" , "Decline, repudiate" , "Say no to - rubbish" , "Turn down, reject" , "Waste, garbage" .)