The periapt of placebos is a common magic item among alchemists and plague doctors alike, many of whom erroneously believe it renders them immune to the dangerous conditions in which they work.
This necklace—often mistaken for a periapt of health or a periapt of proof against poison—inspires its wearer with the utter conviction that he has been rendered immune to both disease and poison. While the necklace imparts no genuine protections, the strength of belief it imparts nonetheless grants its wearer a +2 morale bonus to all Fortitude saving throws against diseases and poisons.
Unless the person identifying a periapt of placebos succeeds at her Spellcraft check by 5 or more, she mistakenly believes it to be a more powerful protective necklace rather than discerning its true nature.
Pathfinder Adventure Path #116: Fangs of War © 2017, Paizo Inc.; Authors: Ron Lundeen, with John Compton, Adam Daigle, Crystal Frasier, Michelle Jones, and Mark Moreland.