Weight: ½ lb.
Estimated Value (Sane Cost Guide): 1,500 gp
DMG Value: 101 gp - 500 gp
While wearing this necklace, you can breathe normally in any environment, and you have advantage on saving throws made against harmful gases and vapors (such as cloudkill and stinking cloud effects, inhaled poisons, and the breath weapons of some dragons).
Source: DMG p182