See a security device with a timing mechanism (5)
I believe the answer is:
clock
'see' is the definition.
(clock can mean to see or notice)
'a security device with a timing mechanism' is the wordplay.
'a security device' becomes 'lock' (I've seen this before).
'with' says to put letters next to each other.
'a timing mechanism' becomes 'c' (I can't justify this - if you can you should believe this answer much more).
'lock' after 'c' is 'CLOCK'.
Can you help me to learn more?
(Other definitions for clock that I've seen before include "Watch" , "Hit" , "Striker" , "Timepiece" , "how to falsify car's mileage" .)