Secret device used with indignation? (4)
I believe the answer is:
wire
'secret device' is the definition.
(concealed listening device)
'with indignation?' is the wordplay.
'with' becomes 'w' (abbreviation).
'indignation?' becomes 'ire' (indignation is a kind of ire).
'w'+'ire'='WIRE'
'used' is the link.
(Other definitions for wire that I've seen before include "See 2" , "See 20" , "Hand signal; breaker" , "Electrical connector" , "Flex" .)