Security device gets secretary and student in place of those accused (7)
I believe the answer is:
padlock
'security device' is the definition.
(device for keeping something secure)
'secretary and student in place of those accused' is the wordplay.
'secretary' becomes 'PA' (abbreviation for personal assistant).
'and' means one lot of letters go next to another.
'student' becomes 'l' (as in L-plates for learner drivers).
'in' indicates putting letters inside.
'place of those accused' becomes 'dock' (the accused is in the dock in a court).
'l' put inside 'dock' is 'dlock'.
'pa'+'dlock'='PADLOCK'
'gets' is the link.
(Other definitions for padlock that I've seen before include "Securing device" , "security measure" , "Security device for chain etc" , "E.g. shed, moneybox, fastener" , "Detachable security device" .)