Golf rookie finally breaking par reveals electronic device (5)
I believe the answer is:
pager
'electronic device' is the definition.
(I know that pager is a type of electronic device)
'golf rookie finally breaking par' is the wordplay.
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'finally' indicates one should take the final letters.
'breaking' is an insertion indicator.
The final letter of 'rookie' is 'e'.
'g'+'e'='ge'
'ge' going into 'par' is 'PAGER'.
'reveals' acts as a link.
(Other definitions for pager that I've seen before include "Electronic messaging device" , "One calling" , "This may summon one" , "Small radio bleeper for contact" , "Way to contact" .)