Smart card contains expensive piece (7)
I believe the answer is:
sidearm
'piece' is the definition.
(I've seen this before)
'smart card contains expensive' is the wordplay.
'smart card' becomes 'SIM' (SIM card in a smart phone).
'contains' is an insertion indicator.
'expensive' becomes 'dear' (similar in meaning).
'sim' going around 'dear' is 'SIDEARM'.
(Other definitions for sidearm that I've seen before include "weapon" , "Officer may carry this" , "Piece" , "One may be fired" .)