What does ring d do in Pokemon mystery dungeon blue rescue team?

The Rescue Ring is an item in Pokémon Mystery Dungeon: Blue Rescue Team and Red Rescue Team that can be used to save a player's life. If a player's HP drops to zero, the Rescue Ring will automatically activate and revive the player with a small amount of HP. Rescue Rings are sometimes rewarded as rewards for clearing dungeons, but can also be purchased at the in-game shop.