ARP signal everyone understood (3-5)

I believe the answer is:

all-clear

'arp signal' is the definition.
(I've seen this before)

'everyone understood' is the wordplay.
'everyone' becomes 'all' (all people).
'understood' becomes 'clear' (is that clear?).
'all'+'clear'='ALL-CLEAR'

(Another definition for all-clear that I've seen is " Signal that danger is past".)

I've seen this clue in The Independent and The Sun.

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