Tomb Raider Silencer challenge objective: Destroy four alarms with Pry Axe in the Shantytown.
The first alarm is on the top of the ripped sunshade in the Shantytown.
The main story leads you to the second part of the Shantytown, where Lara will be ambushed by enemies. They will use an alarm to get reinforcement, and you should destroy it.
Upon destroying the second alarm use a zipline to access the tower where you can find the third alarm. It’s a point when you should complete part of the main story “Find your way to Grim
This alarm can be found on the windmill.