Locating device (5)
I believe the answer is:
radar
'locating device' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for radar that I've seen before include "Equipment for locating objects" , "Measuring device that locates distant objects" , "Range and direction finding equipment" , "Locator that uses a microwave echo" , "Position detector using radio wave pulses" .)