Penny drops – it concealed hidden dangers (8)
I believe the answer is:
pitfalls
'hidden dangers' is the definition.
(I've seen this before)
'penny drops it concealed' is the wordplay.
'penny' becomes 'p' (short for pence).
'drops' becomes 'falls' ('fall' can be a synonym of 'drop').
'concealed' is an insertion indicator.
'p'+'falls'='pfalls'
'pfalls' placed around 'it' is 'PITFALLS'.
(Other definitions for pitfalls that I've seen before include "Unsuspected dangers or difficulties - for miners?" , "Catches" , "Lifts pal from unexpected difficulties or dangers" , "Hidden dangers, booby traps." .)