Silly preset mode restricting key measuring device (11)
I believe the answer is:
speedometer
'device' is the definition.
(speedometer is a kind of device)
'silly preset mode restricting key' is the wordplay.
'silly' indicates anagramming the letters.
'restricting' means one lot of letters goes inside another.
'key' becomes 'e' (a musical key).
'preset'+'mode'='presetmode'
'presetmode' with letters rearranged gives 'speedomter'.
'speedomter' going around 'e' is 'SPEEDOMETER'.
'measuring' is the link.
This may not be correct. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for speedometer that I've seen before include "Dashboard instrument" , "Dashboard dial" , "It tells driver how fast he is going" , "Device giving rate of movement (in car etc)" , "clock" .)