Change your preferences here.
There is a 10% chance that when the holder is hit by an attack that would otherwise cause fainting, it will survive with 1 HP. Can also protect against recoil damage, multi-hit moves, and self-inflicted confusion damage, but not from Future Sight or Doom Desire or from self-induced fainting due to Selfdestruct, Explosion, Memento, Lunar Dance, or Healing Wish. It will not protect against passive damage such as sandstorm or poison.
Unreliable as they come—if you are willing to stake your all on a 10% chance then go ahead. Otherwise, more conventional items will generally serve you better—and won't only give you an advantage once in every ten battles.
Battle Subway, 48 BP.