"listening devices" (4)
I believe the answer is:
ears
'listening devices' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ears that I've seen before include "Seed-bearing parts of corn" , "'''Friends, Romans, countrymen, lend me your ...'' (Julius Caesar) (4)'" , "Sear (anag.)" , "Auditory organs" , "One's hearing aids" .)