Signal to say danger has passed (3,5)
I believe the answer is:
all clear
'signal to say danger has passed' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for all clear that I've seen before include "Signal that it's safe to come out" , "ARP signal" , "I understand everything" , "no longer misunderstood?" , "without any ambiguity" .)