Read a bar code (4)
I believe the answer is:
scan
'read a bar code' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for scan that I've seen before include "Hercule ---, detective" , "Look over (in order to copy?)" , "show in this?" , "Convert (a document) to a digital form" , "Examine quickly" .)