Happy without line, understands devices (7)
I believe the answer is:
gadgets
'happy without line understands devices' is the definition.
I can't tell whether this defines the answer.
'happy without line understands devices' is the wordplay.
'happy' becomes 'glad' ('glad' can be similar in meaning to 'happy').
'without' is a deletion indicator.
'line' becomes 'l'.
'understands devices' becomes 'gets' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'glad' with 'l' removed is 'gad'.
'gad'+'gets'='GADGETS'
Can you help me to learn more?
(Other definitions for gadgets that I've seen before include "jimjams" , "'Devices, gizmos (7)'" , "Ingenious devices" .)