Les abandons hopelessly bad security device (7)
I believe the answer is:
spyhole
'security device' is the definition.
'les abandons hopelessly bad' is the wordplay.
'abandons' suggests deleting specific letters.
'bad' indicates an anagram.
'hopelessly' with 'les' taken out is 'hopesly'.
'hopesly' anagrammed gives 'SPYHOLE'.
(Other definitions for spyhole that I've seen before include "Viewer (e.g. in door)" , "Viewing device" , "Small viewing port" , "feature of door?" .)