Servant chucked, no good with security device (7)
I believe the answer is:
flunkey
'servant' is the definition.
(flunkey is a kind of servant)
'chucked no good with security device' is the wordplay.
I cannot quite see how this works, but
'no' could be 'n' (common abbreviation) and 'n' is present in the answer.
'device' could be 'uke' (uke is a kind of device) and 'uke' is present in the remaining letters.
The remaining letters 'fly' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for flunkey that I've seen before include "Footman or slavish follower" , "Footman - stooge" .)