Back in Hanoi, daring to send a message (5)
I believe the answer is:
radio
'send a message' is the definition.
(I've seen this before)
'back in hanoi daring' is the wordplay.
'back' says the letters should be written backwards.
'in' says the answer is hidden in the clue.
'oidar' is hidden within 'hanoi daring'.
'oidar' reversed gives 'RADIO'.
'to' acts as a link.
(Other definitions for radio that I've seen before include "broadcasting station" , "Wireless broadcast" , "Sound receiver" , "Broadcast receiver" , "Broadcast medium" .)