When depressed, you could find it helps to get over the threshold (8)
I believe the answer is:
doorbell
'threshold' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for doorbell that I've seen before include "Alternative to knocker" , "Entrance ringer" , "Press it to gain access" , "It announces a caller" , "It's rung by visitors" .)