pf2e.fyi
From Pathfinder Impossible Magic, which isn't enabled.

Unnerving

ITEM 7
Price 350 gp
Usage etched onto armor
Bulk —

The sound of weapons clanging against a suit of unnerving armor transforms into an inhuman screech that unsettles enemies and makes them hesitate to attack again. Any creature that hits you with a melee Strike takes a –1 circumstance penalty to its next melee Strike that targets you before the end of your next turn.

Pathfinder Impossible MagicORC