The AFL has reviewed the final passage of play in the Fremantle vs North Melbourne match at Optus Stadium on Saturday.
 
The final siren sounded before the ball goes out of play. The umpire’s decision on the ground was correct.

Fremantle coach Justin Longmuir trusted the umpires got it right in not awarding a free kick after the siren, admitting his team would have been stealing a win or draw if it had been given the chance. 
 
See below the AFL’s ARC vision of the last passage of play that shows the siren sounding while the ball is still in play and includes umpire decision and comms in real time.

Decision-making process regarding the rule. (Right-click to download and view)