Eye ticker (5)
I believe the answer is:
watch
I believe this is a double definition.
'eye' is the first definition.
(I've seen this in another clue)
'ticker' is the second definition.
(I know that ticker can be written as watch)
(Other definitions for watch that I've seen before include "Vigil" , "Keep under observation" , "Timepiece - look out" , "Observe - timepiece" , "See 21" .)